Bring a large pot of salted water to a boil. Add the elbow macaroni and cook according to package directions until al dente. Drain and set aside.

In the same pot, melt the butter over medium heat. Add the flour and whisk continuously for about 2 minutes until it forms a smooth paste and turns slightly golden.

Gradually pour in the milk and heavy cream while whisking constantly to prevent lumps. Continue whisking until the mixture thickens, about 3-4 minutes.

Reduce heat to low. Add the shredded cheddar and mozzarella cheese in batches, stirring until completely melted and smooth. Season with garlic powder, salt, and black pepper.

Add the cooked macaroni back into the pot with the cheese sauce. Stir well to ensure every piece of pasta is coated with the creamy cheese sauce.

Taste and adjust seasoning if needed. If the sauce is too thick, add a splash of milk to reach desired consistency. Serve immediately while hot and creamy.