Preheat your oven to 350°F (175°C).
Cook the macaroni in a large pot of salted boiling water until just al dente, about 7 minutes. Drain and set aside.
In a medium saucepan, melt the 1/4 cup butter over medium heat. Stir in flour and continue cooking for 1 minute.
Gradually whisk in milk until smooth. Bring to a simmer and let thicken, about 2 minutes.
Remove from heat and stir in cheddar, Gruyère, and Parmesan cheeses until melted. Season with salt, pepper, and paprika.
Combine the cooked macaroni and cheese sauce in a large bowl. Transfer to the prepared baking dish.
In a small bowl, mix panko breadcrumbs with 2 tablespoons melted butter. Sprinkle over the mac and cheese.
Bake for 25-30 minutes, or until bubbly and golden brown. Garnish with fresh parsley if desired.