Preheat your oven to 375°F (190°C). Lightly grease a 9x13-inch baking dish. Cook the elbow macaroni in salted water according to package directions until just shy of al dente (about 1-2 minutes less than recommended). Drain well and set aside.

In a large pot or Dutch oven, melt 1/2 cup of butter over medium heat. Once melted, whisk in the flour. Cook for one minute, whisking constantly, to form a smooth roux.

Gradually pour in the warmed milk and heavy cream while whisking continuously to prevent lumps. Continue to cook, stirring frequently, until the sauce thickens enough to coat the back of a spoon, about 5-7 minutes.

Remove the pot from the heat. Add the softened, cubed cream cheese and stir until it melts completely and the sauce is smooth.

Add the shredded cheddar and Gruyère cheeses in handfuls, stirring until each addition is fully melted before adding the next. Stir until the sauce is completely smooth. Add the dry mustard, paprika, garlic powder, salt, and pepper.

Gently fold the cooked macaroni into the cheese sauce until fully coated. Pour the mixture into the prepared baking dish and spread evenly.

For the optional topping, combine the Panko breadcrumbs with 2 tbsp of melted butter in a small bowl. Sprinkle the mixture evenly over the mac and cheese.

Bake for 25-30 minutes, or until the sauce is bubbly and the topping is golden brown and crisp. Let the mac and cheese rest for 10-15 minutes before serving to allow the sauce to set.