Step 1: Sauté the Seafood

1. Preheat oven to 350°F (175°C).
2. Pat shrimp and scallops dry with a paper towel.
3. In a large skillet, melt 1 tablespoon butter over medium heat.
4. Sear shrimp and scallops for 1-2 minutes per side, until lightly golden (do not fully cook).
5. Remove from the skillet and set aside.

Step 2: Make the Creamy Sauce

1. In the same skillet, melt the remaining 1 tablespoon butter over medium heat.
2. Stir in flour, whisking constantly for 1 minute to create a roux.
3. Slowly whisk in white wine, chicken stock, and heavy cream, stirring until smooth.
4. Add Dijon mustard, garlic powder, onion powder, black pepper, and Old Bay seasoning.
5. Simmer for 2-3 minutes, until the sauce thickens slightly.

Step 3: Pre-Bake the Flounder

1. Place flounder fillets in a greased 9×13-inch baking dish.
2. Bake for 5-7 minutes, just until the fish is opaque.
3. Remove from the oven and drain any excess liquid.

Step 4: Assemble the Casserole

1. Arrange the shrimp, scallops, and lump crabmeat over the flounder.
2. Pour the creamy sauce evenly over the seafood.
3. Sprinkle with additional Old Bay seasoning if desired.

Step 5: Bake to Perfection

1. Bake for 15-20 minutes, or until the sauce is bubbly and the seafood is fully cooked.
2. Remove from oven and let rest for 5 minutes before serving.
3. Garnish with chopped Italian parsley and enjoy!