01Preheat oven to 400 degrees F. Cook macaroni according to package directions. Drain cooked macaroni and set aside.
02In a large saucepan over medium heat, melt the butter. Add flour and whisk together to form a paste and cook until lightly brown. Whisk milk in portions until mixture is blended and creamy. Remove from heat.
03Add salt, pepper, mustard, and Old Bay seasoning to milk mixture. Whisk together with 2 cups of shredded cheese until smooth in consistency. Stir in crab and cooked macaroni until well combined.
04Pour mixture in a baking dish. Top with bread crumbs and remaining 1/2 cup cheese. Bake until topping is browned and cheese melts, approximately 30 minutes. Garnish with parsley