1. Preheat your oven to 350°F (175°C). Grease a 9×13-inch baking dish.

2. Cook the elbow macaroni in a large pot of salted boiling water until just al dente. Drain and set aside.

3. In a large saucepan, melt butter over medium heat. Whisk in flour and cook, stirring constantly, for about 1-2 minutes until lightly golden.

4. Gradually pour in milk, whisking constantly until the sauce is smooth. Bring to a simmer and cook until thickened, about 5 minutes.

5. Remove from heat and stir in 3 cups of cheddar and 1 1/2 cups of Gruyère cheese. Stir until fully melted and the sauce is creamy.

6. Add salt, pepper, and paprika (if using).

7. Combine drained macaroni with the cheese sauce. Mix until all noodles are well coated.

8. Transfer half of the mac and cheese to the prepared baking dish. Sprinkle with half the remaining cheeses. Add the rest of the pasta and top with the remaining cheeses.

9. In a small bowl, mix breadcrumbs with a tablespoon of melted butter (optional). Sprinkle evenly over the top.

10. Bake uncovered for 20 minutes or until bubbly. For a golden-brown crust, broil for 2-3 minutes, watching closely.

11. Remove from the oven. Let cool for 10 minutes, then garnish with chopped parsley and serve.