- 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.