Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish or a similar size casserole dish lightly with butter.

Cook the elbow macaroni according to the package directions, making sure to leave it slightly al dente. Drain and set aside.

In a large saucepan over medium heat, melt the unsalted butter. Add the flour, whisking constantly, and cook for 1-2 minutes without letting it brown.

Slowly add the whole milk while continuing to whisk to avoid any lumps. Follow with the heavy cream, continuing to stir until the mixture is smooth and starts to thicken, about 3-5 minutes.

Add the salt, black pepper, mustard powder, and smoked paprika to the milk mixture, whisking until well combined.

Stir in 3 cups of shredded cheddar cheese gradually until melted and the sauce is creamy and smooth.

Add the cooked macaroni to the cheese sauce, stirring until the pasta is well coated.

Pour the macaroni and cheese mixture into the prepared baking dish. Sprinkle the remaining 1 cup of shredded cheddar cheese evenly on top.

If using, sprinkle the breadcrumbs over the cheese topping.

Bake in the preheated oven for 20-25 minutes, or until the cheese is bubbly and the top is lightly browned.

Allow the mac-and-cheese to cool for a few minutes before serving.