Pour the wine into a large saucepan and add the chopped shallot and crushed garlic. Bring the mixture to a boil over high heat, then reduce to a simmer and cook for 2 minutes to infuse the wine with the aromatics.
Add the mussels to the pan, cover tightly with a lid, and return to a boil. Cook for 5–6 minutes, shaking the pan frequently to help the mussels cook evenly, until all the shells have opened wide.
Using a slotted spoon, carefully transfer the opened mussels to a large bowl. Discard any mussels that remain closed after cooking, as these are not safe to eat. Never try to force them open.
Strain the flavorful cooking liquid through a fine sieve into a clean saucepan to remove any grit or shell fragments. Bring it to a boil and let it simmer until it reduces down to about 3 tablespoons of concentrated liquid. Stir in the half-and-half and warm through gently. Add half of the chopped parsley and season with salt and pepper to taste.
Remove and discard the top shell from each mussel, leaving the meat sitting in the bottom shell. Arrange these shells neatly on a large ovenproof serving dish, spacing them out evenly.
Spoon the creamy sauce generously over each mussel, then sprinkle with bread crumbs and drizzle with melted butter for a golden, crispy topping. Place the dish under a preheated hot broiler, positioned about 4 inches from the heat source, and cook for 3–5 minutes until the topping turns golden brown and bubbly.
Remove from the broiler, garnish with the remaining fresh parsley, and serve immediately while the mussels are hot and the topping is still crispy.
