Preheat the oven to 350°F (175°C).
Cook the elbow macaroni according to package instructions until al dente, then drain and set aside.
In a large saucepan, melt ¼ cup unsalted butter over medium heat.
Whisk in the flour and cook for about 1-2 minutes to form a roux.
Gradually whisk in the milk and heavy cream, cooking until the sauce thickens, about 5-7 minutes.
Remove from heat and stir in 3 cups shredded cheddar cheese and mozzarella cheese until melted and smooth.
Season the cheese sauce with salt and ground black pepper.
Combine the cooked macaroni with the cheese sauce and mix well.
Pour the mac and cheese mixture into a greased baking dish.
In a small bowl, mix the panko breadcrumbs with melted butter.
Sprinkle 1 cup cheddar cheese evenly over the top of the macaroni.
Top with the buttery panko breadcrumbs mixture.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and bubbly.
Let it cool for a few minutes before serving.