Keto fish casserole with mushrooms and French mustard

Keto fish casserole with mushrooms and French mustard

So hearty. So satisfying. And so simple to make. If you love fish, mushrooms, and creamy, rich sauces, be prepared to fall head over heels in love with this amazing keto casserole.
June 21 2016 recipe by , photo by , nutritional review by in Recipes, Dinner, Meal

Keto fish casserole with mushrooms and French mustard

So hearty. So satisfying. And so simple to make. If you love fish, mushrooms, and creamy, rich sauces, be prepared to fall head over heels in love with this amazing keto casserole.
USMetric
6 servingservings

Ingredients

Fish casserole
  • 1 lb (6½ cups) 450 g (1.5 liters) mushrooms, cut into wedges
  • 3½ oz. 100 g butter, melted
  • 1 tsp 1 tsp salt
  • pepper, to taste
  • 2 tbsp 2 tbsp fresh parsley
  • 2 cups 475 ml heavy whipping cream
  • 2 tbsp 2 tbsp Dijon mustard
  • 1½ lbs 650 g white fish fillet, for example cod, halibut or Alaskan whitefish (fresh, or frozen)white fish fillets, for example cod, halibut or Alaskan whitefish (fresh, or frozen)
  • 2 cups (8 oz.) 475 ml (230 g) Gouda cheese, shredded, divided
Broccoli (or cauliflower) al dente
  • 1½ lbs (7½ cups) 650 g (1.7 liters) broccoli or cauliflower, cut into florets
  • 3½ oz. 100 g olive oil or butter, melted
  • salt and pepper, for seasoning
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Instructions

Fish casserole

  1. Preheat the oven to 350°F (175°C).
  2. Melt the butter in a large frying pan, over medium heat. Add the mushrooms, salt, and pepper. Fry until softened, for about 5 minutes.
  3. Stir in the parsley, mustard, and heavy cream. Reduce the heat to medium-low and simmer uncovered, for 5-6 minutes to slightly reduce the sauce.
  4. Season the fish with salt and pepper and place in a greased baking dish. Sprinkle 3/4 of the cheese on top, and then cover with the creamed mushroom mixture. Top with the remaining cheese.
  5. Bake uncovered for about 30 minutes if the fish is frozen, or slightly less if it’s fresh. Probe with a sharp knife after 20 minutes; the fish is done if it flakes easily with a fork. And remember that the fish will continue to cook even after you have taken it out of the oven. Meanwhile, make the vegetable side dish.

    6. Broccoli (or cauliflower) al dente

  6. Bring a large pot of lightly salted water to a boil, over high heat. Add the broccoli or cauliflower, and boil for a few minutes, until crisp-tender.
  7. Strain in a colander, and then place in a serving dish. Add the melted butter or olive oil, and toss to coat. Season with salt and pepper to taste, and serve with the fish casserole.

Tip!

Did you know that the stem of broccoli and cauliflower is wonderful, too? Simply peel the rough outer layer off with a sharp knife or a potato peeler. And then cut the stems lengthwise into rods, or dice them. Voila! More cruciferous love!

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💬 Have you tried this recipe?

What did you think? Please share your thoughts in the comment section below!

50 comments

  1. 1
    Nichy
    July 3 2016
    This was delicious. I'm not a seafood fan but thought I'd make this, mainly for my hubby, and I really enjoyed it.
  2. 2
    Jenny
    July 6 2016
    I thought this recipe would be a bit bland with plain white fish, so used smoked cod to add a bit more flavour. It turned out so well.
  3. 3
    Brenda
    July 8 2016
    Absolutely gorgeous, made it with freshly landed north sea cod. I used fennel and basil to flavour the sauce.
  4. 4
    Vicki
    September 27 2016
    Wondering what to use instead of mushrooms - can't stand them cooked - any suggestions?
  5. 5
    Nani
    October 24 2016
    Vicky, same here.... I'm thinking about doing it tomorrow with leek instead.... what do you think?
  6. 6
    Anneline Grobler
    November 29 2016
    This was a wonderful dish. I don't like fish as a rule but thought it might be a good dish for dinner guests and I really liked it:)
    I did however thicken it up a tad with some Xanthan gum...does anyone know the good or bad about this product on a low carb plan??
  7. 7
    Rhonda
    May 13 2017
    What kind of cheese is everyone using?
    Reply: #14
  8. 8
    Stephen
    June 25 2017
    Mature cheddar all the way, as its so flavoursome. If you prefer you could use a milder version.
  9. 9
    andrea
    August 1 2017
    omg, was that delicious! used salmon, as its what we had, fattier, and hubby doesn't like whitefish anyway. :D
    Needs more cream, but oh, so delicious!!! definitely a keeper!
  10. 10
    Letitia
    January 31 2018
    Tasted really good, I had my doubts combining mushroom, mustard and fish, but my pangasius turned out fantastic. I used grated gouda 48+. The cream sauce was a bit too thin, maybe the xanthan gum could solve it. So good I would serve it guests too (it looks very delicious).
  11. 11
    Paul
    April 2 2018
    I cooked this for the first time tonight. Used a Fish Pie Pack from the supermarket which had a mix of cod, salmon and smoked haddock. Also threw in a can of tuna. Tasted amazing, but as others have said the sauce could have been thicker. Will definitely make again!
  12. 12
    Jon
    July 17 2018
    It smells and taste very good... but i didnt get casserole.. Its real soupy, and I simmered the heavy cream for a long time to. Not sure what i did wrong.
  13. 13
    Jim
    July 20 2018
    Made it tonight and followed instructions to the letter!
    Amazing 😉
  14. 14
    Reply to comment #7 by Rhonda
    Una
    September 16 2018

    What kind of cheese is everyone using?

    Rhonda, I am.making this this week and will use the strongest mature cheddar we have in England - No 7 on the packet - either Canadian or English. It's grated in Britain not American shredded!!! 😂 Needs to be a hard cheese not anything that is remotely soft. I never buy already grated cheese as the strength only goes up to No 4 so too mild and easy to grate cheese. Another cheese I would think of using is a good quality Gruyere, which is also a hard and strong delicious cheese. Hope all this helps. Thanks to.everyone who said the sauce was too thin. Will bare that in mind when cooking this.

  15. 15
    Mauretta
    September 28 2018
    This was amazing, My hubby fishes alot so we always have fish in the house and always looking at different ways to cook it and this was so nice! i served mine with cauliflower mash divine!!
  16. 16
    Aidan
    December 4 2018
    Delicious! Favourite dish.
  17. 17
    Sheri Abear
    January 11 2019
    Delicious 😋♥️I used Colby/Jack cheese..
  18. 18
    Jarrah
    January 29 2019
    As Jon said, it was very soupy. Loved the flavour but it wasn’t a casserole
  19. 19
    Jennifer
    February 6 2019
    This was so good. Modified and added some cauli rice since I didnt have enough mushrooms. Sauce thickened beautifully. I also hit it with about 5 minutes of broiler for a crispy top. Two thumbs up from the husband too!
  20. 20
    Hollly
    February 23 2019
    I used an oven friendly saucepan and cooked it on the stove top until the sauce was thickened. Added some cheese to the top and under the broiler for a couple minute. Used a mix of several cheeses but mostly cheddar. Got a thumbs up!
  21. 21
    Anneleen
    March 7 2019
    Fantastic!
  22. 22
    Monika
    March 14 2019
    simply fantastic :-)
  23. 23
    Monica
    March 20 2019
    Could I substitute coconut cream?
    Reply: #24
  24. 24
    Reply to comment #23 by Monica
    Kristin Parker Team Diet Doctor
    March 20 2019

    Could I substitute coconut cream?

    You can try that, it may give a coconut flavor to the dish you may not enjoy but coconut cream is a common sub for heavy cream.

  25. 25
    Carlye Brownell
    March 25 2019
    How many cups is one serving?
    Reply: #26
  26. 26
    Reply to comment #25 by Carlye Brownell
    Kristin Parker Team Diet Doctor
    March 26 2019

    How many cups is one serving?

    That depends on how much your recipe reduces (or doesn't). Final volume can vary. This recipe as written makes 6 servings.

  27. 27
    Janet
    April 27 2019
    we just loved this recipe, thank you.
  28. 28
    Rock
    May 31 2019
    One of our favorite fish recipes! Tastes delicious and easy! Of all things, I add a bay leaf based upon a fish pie recipe in an Irish cookbook. It adds a lot of flavor and complements the mushrooms very nicely.
  29. 29
    Ray Bussey
    July 17 2019
    I added some paprika to the sauce. It was fantastic!
  30. 30
    Tara
    August 4 2019
    Omg this was soooooooo good! Thank you!
  31. 31
    Eva
    August 31 2019
    Very delicate❤️❤️
  32. 32
    Sally
    October 29 2019
    Loved this recipe, used cod as suggested but could use a stronger tasting fish. Deliciousness . 😍❤️
  33. 33
    cindoger1
    February 1 2020
    Coming to y'all from the coast of NC. Turned out fabulous.
  34. 34
    scundif1659
    February 3 2020
    To thicken the sauce I used 8 oz of cream cheese. It was delicious!
  35. 35
    Yvonne
    March 13 2020
    Made this last night, was absolutely delicious, I took note of people saying it was like soup, so only used half the amount of cream, and used cream cheese to make up the other half. Came out lovely and thick just like a casserole should be. Will definitely be making again.
  36. 36
    millie.pupuke
    April 14 2020
    Had this tonight, with cod, husband loves fish, was so delicious, next time I will probably add some smoked fish and maybe leeks and thicken a little with xanthan gum. Definitely a favourite!!
  37. 37
    KarinB
    April 23 2020
    Oh my! This is delicious. I used a tad less cream(1/2 cup less) and more cheese. I used strong mature cheddar. The sauce was the perfect consistency with cheesy gooey-ness... just the way Iike it. To add some colour, I also sprinkled chopped scallions/green onion just before serving.
    Reply: #38
  38. 38
    Reply to comment #37 by KarinB
    Crystal Pullen Team Diet Doctor
    April 23 2020

    Oh my! This is delicious. I used a tad less cream(1/2 cup less) and more cheese. I used strong mature cheddar. The sauce was the perfect consistency with cheesy gooey-ness... just the way Iike it. To add some colour, I also sprinkled chopped scallions/green onion just before serving.

    I am so glad you enjoyed it! I love your description.

  39. 39
    Dawn Tyson
    June 6 2020
    I made this with undyed smoked haddock and it was insanely good! Thank you for the recipe x
    Reply: #40
  40. 40
    Reply to comment #39 by Dawn Tyson
    Kerry Merritt Team Diet Doctor
    June 7 2020

    I made this with undyed smoked haddock and it was insanely good! Thank you for the recipe x

    Great! So glad you enjoyed it!

  41. 41
    Ina
    June 11 2020
    The nutrition value is for 1 serving?
    Reply: #42
  42. 42
    Reply to comment #41 by Ina
    Kristin Parker Team Diet Doctor
    June 12 2020

    The nutrition value is for 1 serving?

    Yes, all of our recipes list the nutrition information per serving.

  43. 43
    emmapheee
    June 16 2020
    Anyone know if this would be suitable for freezing after being cooked?
    Reply: #44
  44. 44
    Reply to comment #43 by emmapheee
    Crystal Pullen Team Diet Doctor
    June 16 2020

    Anyone know if this would be suitable for freezing after being cooked?

    I have not tried freezing this particular dish, but if you allow it to thaw in the refrigerator before reheating slowly, it should be fine.

  45. 45
    susan60
    August 17 2020
    Kind of bland. Needed a lot more mustard. Maybe the cheddar I used wasn't sharp enough, too.

    But did add cauliflower rice to bottom of casserole instead of doing it as a side dish. Yum.

    Reply: #46
  46. 46
    Reply to comment #45 by susan60
    Britta Patterson
    August 17 2020

    Kind of bland. Needed a lot more mustard. Maybe the cheddar I used wasn't sharp enough, too.

    But did add cauliflower rice to bottom of casserole instead of doing it as a side dish. Yum.

    Sorry to hear that you did not find it as flavorful as you had hoped!
    It sounds like a great idea to put the cauliflower rice at the bottom.

  47. 47
    Dave
    September 14 2020
    Tried this last night. It ended up like soup. I even cooked it longer than the recepie said. Thought this would be a good keto recepie to use again but that's not going to happen.
  48. 48
    Valeriia
    September 10 2021
    For those who get this casserole soup-ish. First, choose fish wisely. Often white fish is too watery. When I have only frozen fish, or I see fish is watery, I bake it or fry it for a couple of minutes to reduce the liquid. Second, try good mushrooms, best option is boletus, they add a ton of flavour.
  49. 49
    Rose
    March 30 2022
    Was a bit bland and soupy but some good ideas above on how to improve: add cream cheese and more mustard. Will try again.
  50. 50
    Terri Macklin
    April 28 2022
    I'm in CA and just made this dish using Rock Fish. I also subbed in grated sharp cheddar and some grated parmesan, plus a bit of mozzarella. It was so delish!

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