Preheat the oven to 350°F.
Melt the butter in a large pot over medium heat.
Add the flour and garlic powder, and stir until the mixture is smooth and bubbly.
Slowly whisk in the milk, stirring constantly until the sauce is smooth and thick.
Add the cheddar, Monterey Jack, Gruyere, cayenne pepper, black pepper, and salt. Stir until the cheese is melted and the sauce is smooth.
Add the cooked macaroni and stir until everything is combined.
Pour the macaroni and cheese into an 8x8 baking dish.
In a small bowl, combine the panko breadcrumbs and Parmesan cheese. Sprinkle the mixture over the mac and cheese.
Bake for 25-30 minutes, or until the top is golden brown and the sauce is bubbly.