3/4 cup unsalted butter warm enough to be quite soft
1/3 pound soft Parmigiano
3 ounces Gruyere
3 ounces Edam
3 ounces mozzarella
While the pasta water is heating grind half the Grana and cut the remaining cheeses into thin strips. While the pasta is cooking heat the serving bowl with a ladle of boiling water, and when the pasta is done stir in the strips of cheese and half the butter; keep stirring to melt everything well. Just before serving stir in the remainder of the butter and the grated Grana.