Bring a large pot of well-salted water to a boil over high heat. Add the 12 oz cavatappi and cook for 1 minute less than package directions (about 7 to 8 minutes). Drain without rinsing and set aside.

Melt 3 tbsp unsalted butter in a large heavy-bottomed saucepan over medium heat. Add 3 tbsp all-purpose flour and whisk for 1 minute until the mixture smells nutty and looks pale golden.

Slowly whisk in 2 cups whole milk and 1 cup heavy cream. Increase heat to medium-high and whisk until the sauce thickens and coats the back of a spoon, about 4 to 5 minutes.

Reduce heat to low. Add 2 cups sharp cheddar and 1 cup Gruyère in handfuls, whisking each addition until melted. Stir in 1 tsp Dijon mustard, 1/2 tsp garlic powder, 1/2 tsp onion powder, 1/2 tsp kosher salt, and 1/4 tsp white pepper. Taste and adjust salt.

Add the drained cavatappi to the sauce and fold to coat. Transfer to a broiler-safe 9x13 baking dish and spread into an even layer.

Move an oven rack 6 inches from the broiler and set broiler to high. Toss 1/2 cup panko breadcrumbs with 1 tbsp melted unsalted butter and scatter over the pasta. Broil for 3 to 4 minutes until the breadcrumbs are deep golden brown. Scatter 1 tbsp chopped fresh parsley over the top and serve immediately.