1. Preheat oven to 400 degrees with a rack in the center. Melt 2 tablespoons butter in a medium saucepan over medium heat. Add shallots and cook until soft, about 2 minutes. Add 1 tablespoon water and simmer for 30 seconds. Stir in the cayenne, Old Bay, and dry mustard until well combined. Pour half-and-half into saucepan and bring to a simmer. Slowly whisk in the cream cheese, a few pieces at a time. When the cream cheese is fully incorporated, whisk in the cheddar cheese, a handful at a time. Stir the mixture for 2 minutes. Remove from heat. Add lemon juice and Worcestershire sauce; stir to combine. Stir in crabmeat and half of the parsley.

2. Transfer mixture to an ovenproof baking dish and sprinkle with bread pieces. Dot top of bread pieces with remaining tablespoons butter; sprinkle with paprika. Bake until bread pieces are golden and dip is hot, 18 to 22 minutes. Garnish with remaining 1/4 cup parsley and serve with toast points.