Preheat oven to 350 degrees.

Melt 3 tablespoons of butter in a large saucepan over medium heat.

Remove from heat and whisk in 1/4 cup of flour.

Whisk in 1/2 cup of heavy cream and return to heat.

Add the grated parmesan cheese and stir until creamy.

Remove from heat and add the remaining heavy cream.

Stir in the dry sherry, paprika, Old Bay Seasoning, and cayenne (if using).

Add the sliced mushrooms and minced onion (if using).

Gently fold in the picked and cleaned crabmeat and peeled shrimp.

Spoon the seafood mixture into 6 ramekins.

In a food processor, combine the garlic-flavored croutons and fresh parsley.

Pulse until coarsely ground.

Top each casserole with the crouton mixture.

Drizzle each casserole with 4 tablespoons of melted butter.

Bake in the preheated oven for 20-30 minutes, or until the top is browned and bubbly.