In a large pot, combine 1 cup of dry white wine, 2 smashed garlic cloves, and a few sprigs of fresh thyme. Bring to a gentle simmer over medium heat, then add cleaned mussels and cover. Steam for about 5-7 minutes until the mussels open up. Once cooked, strain the mussels, reserving the delicious liquid for later use.

In a saucepan, melt 3 tablespoons of unsalted butter over medium heat. Add 1 finely minced shallot and sauté for about 3-4 minutes until translucent. Stir in 3 tablespoons of flour to form a roux, cooking for 1-2 minutes until golden. Gradually whisk in the reserved mussel liquid, 1 cup of seafood stock, and 1 cup of heavy cream; simmer for 5-7 minutes, stirring until thickened.

Gently fold in 1 pound each of shrimp, scallops, and cubed white fish into the béchamel sauce. Cook for about 3-4 minutes, stirring occasionally, until the seafood appears just opaque. Afterwards, add the steamed mussels and a handful of chopped fresh parsley, stirring to incorporate everything evenly.

Preheat your oven to 400°F (200°C). Spoon the creamy seafood mixture into individual ramekins or a single baking dish, spreading it evenly.

In a small bowl, mix together 1 cup of breadcrumbs and 1 cup of grated Gruyère cheese, along with 2 tablespoons of melted butter. Evenly sprinkle this mixture over the assembled seafood to create a crispy crust.

Bake for 12-15 minutes, or until the top is golden brown and bubbling. Broil for an additional 2-3 minutes if desired.