Preheat oven to 375°F; grease a 9x13-inch dish.
Cook pasta according to package until al dente; drain and set aside.
Melt 4 tablespoons butter in a large pot over medium; whisk in flour and cook 1 minute until golden.
Gradually whisk in milk; cook about 5 minutes until thickened, stirring constantly.
Remove from heat; stir in cheddar, Gruyère, and fontina until melted and smooth.
Season with salt, pepper, and garlic powder; fold in pasta to coat well.
Spread evenly in dish.
Combine panko, melted butter, and Parmesan; sprinkle over top.
Bake 25-30 minutes until golden brown and bubbly; rest 5 minutes before serving.