Flounder Fillets a la Moutarde Recipe

Flounder Fillets à la Moutarde:

If you’re in the mood for something simple, elegant, and packed with flavor, this Flounder à la Moutarde (flounder with mustard sauce) is exactly what you need. It’s a French-inspired dish that sounds fancy but is surprisingly easy to make at home.

Think flaky, delicate flounder fillets baked under a creamy, tangy mustard sauce that’s rich without being heavy. The mustard gives it a sharp kick, while a touch of cream smooths everything out beautifully.

This recipe is perfect for a weeknight dinner when you want something quick but impressive or when guests are coming and you want to serve a restaurant-style dish without breaking a sweat. The fish cooks fast, and the sauce comes together in just a few minutes. You can even prep parts of it ahead of time.

Serve it with roasted potatoes, steamed asparagus, or a crisp green salad, and you’ve got a special meal that doesn’t ask too much from you in the kitchen. Whether you’re a mustard lover or just looking to shake up your seafood routine, this flounder mortarde will hit the spot. Let’s dive into how it’s done—you’re going to want this one on repeat.

This recipe calls for eight small, skinless, boneless flounder fillets, but at my fish market, they only had a large fluke fillet weighing in at about 1-1/3 pounds. I’m not sure where you could find 8 small flounder fillets totaling 1 pound, with the minimum size allowed to be kept at 18 inches. Maybe he means cutting a large fillet into smaller ones.

Note: Be sure to read my post called Fluke or Flounder – What’s the Difference? I think you’ll find it both informative and interesting.

Print Recipe

Flounder Fillets a la Moutarde Recipe

Prep Time15

Cook Time3

Total Time18

Course: Main Course

Cuisine: American, French

Servings: 4 people

Ingredients

8 small skinless, boneless flounder fillets, about 1¼ pounds
salt & pepper to taste
1 tablespoon peanut oil vegetable or corn oil
2 tablespoons mayonnaise preferably homemade
1 tablespoon imported mustard such as Dijon or Dusseldorf
2 teaspoons parsley finely chopped
4 lemon wedges

Instructions

Start by taking the fish out of the refrigerator while you prep the ingredients and preheat the broiler.
Before preheating the broiler, be sure to get the top oven rack into a position so the fish is about 3 to 4 inches from the broiler heat source. You don't want to be messing with the rack after it gets hot.
In a medium sized bowl, mix the mayonnaise and mustard and stir in the parsley.
Place the flounder fillets onto a baking sheet. I sprayed my baking sheet with a little oil first to prevent sticking.
Brush the mayo/mustard mix evenly over the fillet(s) and place the pan under the broiler about 3 to 4 inches from the heat source.
The recipe says to "broil for about 1 minute or until golden brown on top and the fish is just cooked through." Now maybe Craig Claiborne's flounder fillets were thinner than mine, but I found it took 2 to 3 minutes for them to be cooked through so keep a close watch on them when cooking.
Serve with potatoes or rice, a favorite vegetable and don't forget to add the lemon wedges.

Side Dish Suggestions

Side Dish	Why It Works
Steamed Asparagus	Its mild, grassy flavor balances the richness of the mustard-cream sauce.
Buttered New Potatoes	Creamy and earthy, these potatoes soak up the sauce and add comforting texture.
Garlic Green Beans	Adds a crisp, fresh contrast to the tender fish and tangy sauce.
Lemon Rice Pilaf	The citrus notes brighten the dish and pair naturally with seafood.
Crusty French Bread	Perfect for sopping up the mustard sauce—simple and satisfying.
Celery Root Purée	A silky, slightly sweet base that complements the sharpness of the mustard.
Mixed Greens Salad	Light and peppery greens (like arugula) cleanse the palate and keep things fresh.
Ratatouille	Adds color, heartiness, and French flair to the plate without overpowering it.
Sautéed Spinach	Soft and earthy, it absorbs sauce nicely and keeps the plate balanced.
Herbed Couscous	Light, fluffy, and quick—ideal for soaking up flavors without stealing the show.

Here’s my big old fluke fillet. Well I think it’s fluke and not flounder. Be sure to take it out of the refrigerator in advance of cooking so you’re not sticking a cold piece of fish under the broiler.

Here’s my mayo, mustard and parsley mixture to spread all over the fish.

After placing the fish on a roasting pan, season it with salt and pepper to taste. Spread the mayonnaise, mustard, and parsley coating on top of the fish.