Preheat oven to 350˚F.

Thaw crawfish tails; drain liquid and reserve. Drain macaroni well and place in a large mixing bowl with 3 cups of cheddar, salt, pepper, mustard, and hot sauce.

Place a heavy saucepan over medium heat. Add butter and melt; add minced garlic and sauté until fragrant, 1 to 2 minutes. Sprinkle flour over garlic mixture and whisk to blend; slowly pour in half & half and reserved crawfish liquid, whisking briskly. Bring to a boil and hold at a hard simmer for 3 minutes while whisking constantly. Remove from heat and stir in crawfish tails. Fold crawfish and sauce into the pasta mixture; taste and adjust seasoning.

Pour mixture into a buttered 13x9-inch baking dish, dot with butter, and top with remaining 2 cups of cheddar. Transfer to oven (middle rack) and bake until golden, about 50 minutes. For a darker crust, broil for a few minutes, watching carefully.