Fishy Prep: Give those fish fillets a nice rinse, pat ’em dry, and set them aside like royalty.
Mornay Sauce Time: In a saucepan, melt 2 tablespoons of butter. Stir in the flour, and make sure you’ve got a smooth paste going. Now, gradually add that creamy milk, stirring like there’s no tomorrow. Once thickened, throw in the cheese, mustard, and nutmeg. Give it a good mix until it’s all smooth and dreamy. Season it up with some salt and pepper.
Get Baking: Crank up that oven to 375°F (190°C). Lay the fish fillets in a baking dish, and smother them with your amazing sauce. Mix the remaining butter (melted) with breadcrumbs and sprinkle over the top for that crispy finish.
Bake it Real Good: Pop it in the oven for 20-25 minutes. You’re aiming for a golden, bubbly top. Finish with parsley sprinkles, and voila!