Preheat the oven to 325°F. Grease a 9 x 13-inch baking dish. If you plan to brown the topping under the broiler, choose a dish that is explicitly broiler-safe.

Bring a large pot of salted water to a boil. Cook the elbow macaroni for 1 minute less than the package directions for al dente; the pasta should still have a little bite.

Drain the pasta and toss it with a drizzle of olive oil to prevent sticking.

While the pasta cooks, melt the butter in a large Dutch oven or heavy pot over medium heat.

Add the flour to the melted butter and cook, whisking constantly, for 1 minute.

Gradually whisk in the milk and half-and-half, adding a small amount at first and whisking until smooth before adding more.

Bring the sauce just to a gentle boil over medium heat, whisking constantly, until it coats a spoon. Remove the pot from the heat before adding the cheese.

Whisk in the Worcestershire sauce.

Gradually stir in all 12 ounces of cubed Velveeta and 1 1/2 cups of the grated sharp cheddar. Stir until melted and smooth; reserve the remaining 1 1/2 cups cheddar for the topping.

Stir in the salt, dry mustard, black pepper, and nutmeg.

Add the cooked and drained pasta to the cheese sauce. Stir until the macaroni is fully coated.

Transfer the macaroni and cheese mixture to the prepared baking dish.

Sprinkle the remaining 1 ½ cups grated sharp cheddar cheese evenly over the top.

Bake at 325°F for about 15 minutes, until the topping has melted, the center is hot, and the edges are bubbling. Avoid baking until the sauce looks dry or the pasta is firm.

Optional: if your baking dish is broiler-safe, broil for 2 to 5 minutes to brown the topping, watching continuously. Skip broiling if your dish is not broiler-safe.

Let the mac and cheese rest for a few minutes, then serve while the sauce is still soft and creamy.