Deviled Crab with Sherry Sauce

Preheat oven to 450 °F. Remove crabmeat from shell, discarding cartilage, and cut meat into 1/2-inch pieces. Melt 2 tablespoons butter in a 1 1/2-quart heavy saucepan over moderately low heat, then add flour and cook, whisking, 2 minutes. Add milk in a slow stream, whisking, then add garlic and bring to a boil, whisking. Reduce heat and simmer, whisking, until béchamel is thickened, about 3 minutes. Remove from heat and discard garlic. Whisk together yolks, Sherry, mustard, nutmeg, cayenne, and salt in a bowl, then add hot béchamel in a slow stream, whisking. Pour mixture into saucepan and cook over very low heat, whisking constantly, until an instant-read thermometer registers 160 °F, about 2 minutes. Remove from heat and gently stir in crabmeat and parsley. Divide mixture among 6 (4-ounce) ramekins. Melt remaining 2 tablespoons butter and cool slightly. Stir together melted butter, bread crumbs, and cheese with a fork, then sprinkle over crab. Put ramekins in a shallow baking pan and bake in upper third of oven until crab is bubbling and crumbs are golden brown, about 5 minutes.