1. 1. Cook the Pasta: Bring a large pot of salted water to a rolling boil. Add the elbow macaroni and cook according to package directions until al dente. This usually takes about 7-9 minutes. Drain the pasta well and set aside. Do not rinse the pasta.

2. 2. Prepare the Butternut Squash Puree: If you haven’t already, ensure your butternut squash is cooked and pureed. If roasting, cut the squash in half, scoop out the seeds, brush with a little olive oil, and roast at 400 F (200 C) for 30-40 minutes until very tender. Scoop out the flesh and puree until smooth. If using canned, simply measure out 2 cups.

3. 3. Start the Roux: In a large, heavy-bottomed pot or Dutch oven, melt the unsalted butter over medium heat. Once melted, sprinkle in the all-purpose flour, whisking constantly for 1-2 minutes until a smooth paste (roux) forms and it smells slightly toasty. This is crucial for thickening your sauce.

4. 4. Build the Cheese Sauce Base: Gradually whisk in the warmed whole milk, a little at a time, making sure to incorporate each addition fully before adding more. Continue whisking until the sauce is smooth and begins to thicken, about 5-7 minutes. It should be thick enough to coat the back of a spoon.

5. 5. Add Flavor and Squash: Remove the pot from the heat. Stir in the salt, black pepper, ground nutmeg, and the butternut squash puree. Mix until everything is well combined and the sauce has a uniform orange color.

6. 6. Melt the Cheese: Add the shredded sharp cheddar cheese and Gruyere cheese (if using) to the sauce, stirring until all the cheese is completely melted and the sauce is smooth and creamy. Taste and adjust seasonings if necessary.

7. 7. Combine and Bake: Add the drained cooked macaroni to the cheese sauce, stirring gently until all the pasta is evenly coated. Pour the mixture into a 9×13-inch baking dish. If desired, sprinkle the top with grated Parmesan cheese and panko breadcrumbs for a crispy crust.

8. 8. Bake to Golden Perfection: Bake in a preheated oven at 375 F (190 C) for 20-25 minutes, or until the mac and cheese is bubbly around the edges and the topping is golden brown. Let it rest for a few minutes before serving.