Step 1: Bring a large pot of salted water to a rolling boil. Add your chosen pasta (elbow macaroni, shells, or cavatappi). Cook according to package directions until al dente, about 7-8 minutes. It should still have a slight bite, as it will continue to cook in the oven. Drain well and set aside. Do not rinse the pasta; the starch helps the sauce cling better.
Step 2: In a large, heavy-bottomed pot or Dutch oven, melt 1/2 cup of unsalted butter over medium heat. Once melted and slightly foamy, sprinkle in the all-purpose flour. Whisk continuously for 2-3 minutes to create a smooth roux. This step is crucial for thickening your sauce and cooking out the raw flour taste.
Step 3: Gradually whisk in the whole milk and heavy cream, a little at a time, ensuring each addition is fully incorporated before adding more. This prevents lumps. Continue whisking until the mixture is smooth and begins to thicken, about 5-7 minutes. Bring it to a gentle simmer, but do not boil vigorously.
Step 4: Reduce the heat to low. Add the grated sharp cheddar cheese, Gruyère cheese, and smoked gouda (if using) to the sauce. Stir constantly until all the cheese is melted and the sauce is smooth and creamy. Season with Dijon mustard, Worcestershire sauce, salt, black pepper, and a pinch of nutmeg. Taste and adjust seasonings as needed.
Step 5: Gently fold the cooked, drained pasta into the cheese sauce until every noodle is thoroughly coated.
Step 6: Preheat your oven to 375°F (190°C). Lightly butter a 9x13 inch baking dish. Pour the mac and cheese mixture into the prepared baking dish, spreading it evenly.
Step 7: In a small bowl, combine the panko breadcrumbs with the remaining 2 tbsp of melted butter. Sprinkle this mixture evenly over the top of the mac and cheese.
Step 8: Bake for 25-30 minutes, or until the mac and cheese is bubbly around the edges and the breadcrumb topping is golden brown and crispy. Let it rest for 5-10 minutes before serving. This allows the sauce to set slightly, preventing it from being too runny.