Bring a large pot of water to a boil. Add the pasta and cook according to the package directions. Remove the pasta from the heat. Drain, then pour it back into the hot pot.
Add the milk and butter to the pot. Stir well, until the butter is melted.
Add the cheeses. Stir well, until the cheese is melted. If needed, place the pot over medium heat to speed up the cheese-melting process.