Grate all cheeses together. Cook the past, following packet directions. In a pan large enough to take all the pasta, heat 25 g of the butter. Drain the pasta, keeping a small quantity of the pasta water for the sauce. Stir the rest of the butter and the cheeses into the pan. Once the cheese begins to melt, remove it from the heat. It is important to keep stirring during this process. If the sauce seems too dry, add a little of the reserved pasta water.
Serve immediately. Season with black pepper to taste.
