Begin by steaming clean mussels in a pot with a splash of dry white wine, minced garlic, and fresh thyme. Cover and cook for 4-6 minutes until the mussels open.

In a medium saucepan, melt 2 tablespoons of unsalted butter over medium heat. Add minced shallots and sauté until translucent, about 3 minutes.

Stir in 2 tablespoons of flour, cooking for 1-2 minutes until golden to create a roux.

Gradually whisk in the reserved mussel liquid, another splash of dry white wine, and 1 cup of heavy cream into the roux, stirring continuously. Simmer for 5-6 minutes until thickened.

Gently add the shrimp, scallops, and cubed white fish into the creamy sauce, poaching until just opaque, about 3-4 minutes. Fold in mussels and chopped parsley.

Preheat your oven to 400°F (200°C) while spooning the seafood mixture into ramekins or a baking dish.

In a mixing bowl, combine panko breadcrumbs, 1 cup shredded Gruyère cheese, and 2 tablespoons melted butter. Mix well.

Sprinkle the topping over the seafood in each ramekin. Bake for 12-15 minutes until golden and bubbling.