Follow these detailed instructions carefully to create the ultimate baked three-cheese mac and cheese that will impress everyone. Each step is important for achieving the perfect texture and flavor.

1. Preheat Your Oven and Prepare Baking Dish: Preheat your oven to 375°F (190°C). Grease a 9×13 inch baking dish with butter or cooking spray. This prevents the mac and cheese from sticking and makes serving easier.
2. Cook the Macaroni: Cook the elbow macaroni according to package directions for al dente. It’s crucial not to overcook the pasta, as it will continue to cook in the oven and can become mushy. Drain the macaroni thoroughly and set aside. Rinsing with cold water is optional; some prefer to rinse to stop the cooking process completely, while others believe it washes away some starch that helps the sauce adhere. For this recipe, draining well is sufficient.
3. Make the Roux: In a large saucepan or Dutch oven over medium heat, melt the butter. Once melted, add the all-purpose flour and whisk constantly for 1-2 minutes until the mixture is smooth and pale golden. This is your roux, the base for the creamy cheese sauce. Cooking the roux properly is essential to avoid a floury taste in the final dish.
4. Create the Béchamel Sauce: Gradually whisk in the whole milk, about ½ cup at a time, ensuring each addition is fully incorporated before adding more. Continue whisking constantly to prevent lumps. Once all the milk is added, whisk in the heavy cream. Increase the heat to medium-high and bring the mixture to a simmer, stirring occasionally. Simmer for 5-7 minutes, or until the sauce has thickened slightly and can coat the back of a spoon. This cooking process cooks out the flour and creates a smooth, creamy béchamel sauce.
5. Infuse with Flavor: Remove the saucepan from the heat. Stir in the Dijon mustard and Worcestershire sauce. Season with salt and freshly ground black pepper to taste. Start with about 1 teaspoon of salt and ½ teaspoon of black pepper, and then adjust according to your preference. Remember that the cheese will also add saltiness.
6. Melt in the Cheeses: Gradually add the shredded sharp cheddar cheese, shredded Gruyere cheese, and grated Parmesan cheese to the hot sauce, stirring constantly until all the cheese is completely melted and the sauce is smooth and luscious. Adding the cheese gradually ensures it melts evenly and smoothly into the sauce. Stir until you have a beautiful, creamy cheese sauce.
7. Combine Sauce and Macaroni: Add the cooked and drained macaroni to the cheese sauce in the saucepan. Stir gently to coat the macaroni evenly with the cheese sauce. Ensure every piece of macaroni is generously coated in the creamy cheese mixture.
8. Transfer to Baking Dish and Bake: Pour the mac and cheese mixture into the prepared baking dish, spreading it out evenly. If desired, sprinkle a little extra shredded cheddar and Parmesan cheese on top for an extra cheesy crust.
9. Bake to Golden Perfection: Bake in the preheated oven for 20-25 minutes, or until the mac and cheese is bubbly and golden brown on top. The baking time may vary slightly depending on your oven, so keep an eye on it. You want a beautiful golden crust and a bubbly, heated-through center.
10. Rest and Serve: Remove the baked mac and cheese from the oven and let it rest for 5-10 minutes before serving. This allows the sauce to set slightly and makes it easier to serve. Resting also helps prevent the cheese sauce from being too runny. Garnish with a sprinkle of paprika, if desired, and serve hot.