STEP 1: Prepare the Oven and Dish

1. Preheat your oven to 375°F (190°C).

2. Lightly butter a medium baking dish or individual ramekins.

3. Set aside.

STEP 2: Prepare the Seafood

1. Rinse the scallops and shrimp under cold water.

2. Pat them completely dry with paper towels (this is very important to avoid excess liquid).

3. If scallops are large, cut them in half.

4. Arrange the scallops and shrimp evenly in the prepared baking dish.

5. Lightly season with salt and black pepper.

6. Set aside.

STEP 3: Make the Creamy Sauce

1. In a saucepan over medium heat, melt the unsalted butter.

2. Add the minced garlic and finely chopped shallot (or onion).

3. Cook for 2–3 minutes, stirring gently, until soft and fragrant (do not brown).

4. Sprinkle the flour over the butter mixture and stir constantly for 1 minute to form a smooth roux.

5. Slowly pour in the milk or cream while whisking continuously.

6. Cook and whisk until the sauce thickens and becomes smooth.

7. Season with:

   • Salt

   • Black pepper

   • A pinch of nutmeg (optional)

8. Taste and adjust seasoning, then remove from heat.

STEP 4: Assemble the Gratin

1. Pour the warm sauce evenly over the scallops and shrimp.

2. Gently shake the dish so the sauce settles around the seafood.

STEP 5: Add the Topping

1. In a small bowl, mix:

   • Grated cheese (Gruyère, Parmesan, or both)

   • Breadcrumbs (optional)

2. Sprinkle the mixture evenly over the top.

3. Finish with chopped parsley or fresh herbs.

STEP 6: Bake

1. Place the dish in the preheated oven.

2. Bake for 20–25 minutes, until:

   • The sauce is bubbling

   • The top is golden brown

   • The seafood is just cooked through

3. (Optional) Broil for 2–3 minutes for extra browning—watch carefully.

STEP 7: Rest and Serve

1. Remove from the oven and let rest for 5 minutes.

2. Serve hot with crusty bread, rice, or a fresh green salad.