Bring a large pot of salted water to a boil and cook the elbow macaroni according to package directions until tender but firm.
Drain the pasta and set aside while you prepare the cheese sauce.
Pour the whole milk or heavy cream into a medium saucepan and warm it over medium heat; avoid boiling.
Add the unsalted butter to the warm milk and stir until fully melted.
Incorporate the shredded cheddar, mozzarella, and Parmesan cheeses into the milk mixture, stirring gently until everything is smooth and melted.
Blend in the sour cream, garlic powder, and mustard powder if using, then season with salt and pepper to taste.
Stir the cooked macaroni into the cheesy sauce, ensuring each piece is well coated and creamy.
Optionally, transfer to a baking dish, sprinkle breadcrumbs on top, and broil for a few minutes until golden and crispy.
Garnish with freshly chopped parsley before serving for a fresh finish.
