Bring a large pot of salted water to a boil while you make the sauce. In a medium saucepan, melt the butter over medium heat. Add the flour and stir to combine. Cook for 2-3 minutes.
4 Tablespoons unsalted butter, 1/4 cup all purpose flour
Add the garlic, onion powder, ground mustard, salt, and pepper. Cook for 1-2 minutes or until fragrant. It will have the consistency of a paste.
1 teaspoon granulated garlic, onion powder, & ground mustard, 1/2 teaspoon Morton kosher salt*, fresh cracked black pepper
Reduce the heat to medium-low. While whisking, slowly pour in about 1/2 cup of the milk. The milk should absorb quickly and thicken.
2 1/2 cups milk*
Repeat this process by adding about 1/2 cup of milk and whisk until combined with the remaining milk. This will prevent the sauce from becoming grainy. Stir in the hot sauce.
1-2 teaspoons hot sauce
Reduce the heat to low. Boil the pasta for about 1 minute less than the shortest time instructed on the back of the package. While the pasta is boiling, remove the sauce from the heat and immediately stir in the cheddar and pepper jack, reserving some for topping if desired.
8 ounces (2 cups) extra sharp white cheddar cheese, shredded, 8 ounces dried elbow pasta, 4 ounces (1 cups) pepper jack cheese, shredded*
Strain the pasta and gently fold it into the sauce. Set aside. Taste and add salt if needed.
In a medium mixing bowl, combine the panko, parmesan, melted butter, and garlic. Set aside.
1/2 cup panko breadcrumbs, 1/2 cup parmigiano reggiano, 3 Tablespoons salted butter, melted, 1/2 teaspoon granulated garlic
Grease a medium baking dish. Transfer the pasta to the greased dish.
Sprinkle the cheese on top of the pasta.
Sprinkle the panko topping on top of the cheese.
Bake for 12-15 minutes. Broil if desired to brown the top. Do not overbake the pasta, or the casserole will dry out.