Step 1: Cook the Pasta: Bring a large pot of salted water to a boil. Cook pasta until al dente, about 1–2 minutes less than package instructions. Drain and set aside.
Step 2: Make the Cheese Sauce: In a medium saucepan, melt butter over medium heat. Whisk in flour and cook for 1–2 minutes until lightly golden. Slowly whisk in warm milk and cream, stirring constantly until smooth and thickened. Stir in Dijon mustard, salt, pepper, and paprika. Remove from heat and fold in cheddar, Gruyère, mozzarella, and Parmesan until melted and creamy.
Step 3: Combine Pasta and Cheese: Add cooked pasta to the cheese sauce, stirring gently to coat evenly.
Step 4: Prepare the Topping: In a small bowl, combine breadcrumbs, melted butter, Parmesan, and paprika. Mix well.
Step 5: Assemble the Bake: Preheat oven to 375°F (190°C). Transfer cheesy pasta into a greased 9x13-inch baking dish. Evenly sprinkle the breadcrumb topping over the pasta.
Step 6: Bake: Bake for 25–30 minutes, or until the top is golden brown and crispy. Let rest 5 minutes before serving to allow sauce to set.