Preheat your oven to 400°F (200°C).

In a large skillet, melt 2 tbsp of butter over medium heat. Add the chopped shallot and sauté for 2-3 minutes until softened. Add the minced garlic and sliced mushrooms and cook for another 5-7 minutes, until the mushrooms have released their liquid and started to brown.

Sprinkle the flour over the vegetables and stir constantly for 1 minute to form a roux.

Slowly pour in the white wine to deglaze the pan, scraping up any bits from the bottom. Allow it to simmer for 1 minute.

Gradually whisk in the heavy cream and fish broth until the sauce is smooth. Bring to a gentle simmer and cook for 3-5 minutes, stirring occasionally, until it thickens. Remove from heat and stir in the fresh parsley, salt, and pepper.

In a separate skillet, melt the remaining 1 tbsp of butter over medium-high heat. Add the shrimp and scallops in a single layer and sear for 60-90 seconds per side. They should not be fully cooked.

Gently fold the seared seafood into the cream sauce. Divide the mixture evenly among 4 individual ramekins.

In a small bowl, combine the shredded Gruyère cheese and Panko breadcrumbs. Sprinkle this mixture evenly over the top of each cassolette.

Place the ramekins on a baking sheet and bake for 15-20 minutes, or until the sauce is bubbly and the topping is golden brown. Let them rest for a few minutes before serving.