Preheat oven to 375°F. Cook pasta according to package directions for 5-7 minutes or until it is a little soft but underdone. Drain and rinse the pasta and set aside.
Process the bread in a food processor until it forms small crumbs. Melt 1 tablespoon butter in a small bowl. Add the breadcrumbs and toss to combine. Add the parsley, garlic powder, Parmesan and ½ teaspoon salt to the crumbs and set aside.
In a small bowl combine the milk and cream and set aside. In a medium saucepan melt the remaining 3 tablespoons butter over medium heat. Whisk in the flour and heat until bubbly. Continuing whisking and cook for 1 minute. Slowly add the milk mixture, whisking continuously until smooth. Cook until the milk has thickened enough to coat the back of a spoon.
Remove the saucepan from the heat and add the cayenne, Old Bay, mustard and ½ teaspoon salt. Stir in the cheese until melted. Check seasonings and add salt if needed.
In a large bowl combine the pasta, cheese sauce and crab meat together taking care not to break up all the crab lumps. Butter or lightly grease a 1 ½ quart casserole dish. Pour the macaroni and cheese into the casserole dish and sprinkle the bread crumbs on top. Bake 25-30 minutes or until the top is brown and macaroni is bubbly. If the topping browns too quickly cover loosely with foil.
Notes
(adapted from a recipe by Jodiemo as posted on Tasty Kitchen)
Nutrition information is calculated using an ingredient database and should be considered an estimate. When multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.