Melt 2 tablespoons butter in a small bowl in microwave. Generously coat each fillet with salt and pepper; then brush with melted butter. Add seasoned fillets, presentation side down, to a very hot cast-iron skillet, and sear to get a nice crust, approximately 1 to 2 minutes. Carefully turn and sear other side, about 3 minutes. Remove from heat and set aside. Place a large skillet over medium heat. Cook bacon until crispy. Remove bacon from pan; add remaining butter. Add onions and garlic, and cook for 3 minutes or until onions are translucent. Add bell pepper, celery and mushrooms; cook an additional 3 minutes. Add shrimp and cook for 3 minutes. Dust shrimp mixture with flour, and stir to coat evenly; continue to cook for 2 minutes. Stir in heavy cream and chicken stock; cook until sauce thickens. Add Parmesan cheese, and stir to combine. Add cayenne pepper, and season with salt, pepper and sherry to taste. Spoon sauce over cooked fillets, and garnish with parsley if desired.