Preheat your oven to 350°F (175°C) and grease a large baking dish with butter or cooking spray.

Bring salted water to a rolling boil in a large pot, add elbow macaroni, and cook for 6-8 minutes until al dente. Drain and set aside.

In a medium saucepan, melt 4 tablespoons of unsalted butter over medium heat. Whisk in 4 tablespoons of all-purpose flour and cook for 2 minutes.

Gradually add 3 cups of whole milk, whisking constantly for about 5 minutes until thickened.

Reduce heat to low and stir in 2 cups of sharp cheddar and 1 cup of Gruyère until melted and smooth.

Combine the drained macaroni with the cheese sauce, mixing until coated.

Transfer the mixture to the greased baking dish, sprinkle panko breadcrumbs on top, and bake for 25-30 minutes until golden and bubbly.

Let the dish rest for 10 minutes before serving.