Directions

1. Heat the oven to 375 degrees. Spray a 1 1/2-quart casserole dish with cooking spray; set aside.
   
2. Place bread pieces into a food processor and pulse 10 times until coarse crumbs. In a small bowl melt 1 tablespoon butter in the microwave. Add bread crumbs to butter and mix well. Set the breadcrumbs aside.
   
3. Fill a large pot with water. Bring to a boil. Add macaroni; cook 3 fewer minutes than manufacturer's directions, until outside of pasta is cooked and inside is underdone. Transfer the macaroni to a colander, and drain well.
   
4. While pasta is cooking, melt remaining 3 tablespoons butter in medium pot. When butter is melted, add flour. Cook, stirring, 1 minute. Slowly pour milk into flour-butter mixture while whisking. Continue cooking, whisking constantly, until the mixture bubbles and becomes thick about 5 minutes.
   
5. Remove the pot from the heat. Stir in salt, nutmeg, black pepper, cayenne pepper, Tabasco sauce, 1 1/2 cups cheddar, and 3/4 cup Gruyere. Once cheese has melted, add macaroni and mix well.
   
6. Pour the mixture into the prepared casserole dish. Sprinkle remaining 3/4 cup cheddar and 1/4 cup Gruyere; scatter breadcrumbs over the top. Bake until browned on top, about 30 minutes. Transfer dish to a wire rack to cool for 5 minutes; serve.