Preheat your oven to 350°F (175°C).
In a large pot, bring salted water to a boil. Add the elbow macaroni and cook according to package instructions until al dente. Drain and set aside.
In a medium saucepan over medium heat, melt the 4 tablespoons of unsalted butter. Once melted, whisk in the flour and cook for about 1 minute, stirring continuously.
Gradually add the milk to the flour mixture, whisking constantly to prevent lumps from forming. Cook for about 5-7 minutes until the mixture thickens.
Remove from heat and stir in the shredded cheddar and mozzarella cheese until melted and smooth. Season with salt, black pepper, and paprika.
Add the cooked macaroni to the cheese sauce and stir until well combined.
Pour the macaroni and cheese mixture into a greased 3-quart baking dish.
In a small bowl, combine the bread crumbs with 2 tablespoons of melted butter, then sprinkle the mixture evenly over the mac and cheese.
Bake in the preheated oven for 20-25 minutes or until the top is golden brown and crispy.
Allow to cool slightly before serving.