Bring a large pot of salted water to a boil. Add pasta and cook according to the package instructions until al dente. Reserve ½ cup of pasta water, then drain the pasta using a colander.

While the pasta is cooking, melt the butter in a large skillet over medium heat. Add the flour and whisk constantly for 1 minute to form a smooth roux.

Gradually pour in the milk, whisking to prevent lumps. Bring to a gentle simmer and cook until the sauce thickens, about 3–5 minutes.

Add the cheddar, mozzarella, and parmesan cheeses to the sauce. Stir until the cheeses are fully melted and the sauce is smooth. Add salt, black pepper, and optional garlic powder to taste.

Toss the drained pasta into the cheese sauce. Mix until all the pasta is evenly coated. If the sauce is too thick, add a splash of reserved pasta water to achieve your desired consistency.

Serve hot, sprinkled with extra parmesan if desired.