Four cheeses and one balance
Quattro formaggi is Italian alchemy: one cheese for sharpness (Gorgonzola), one for sweetness (Fontina or mozzarella), one for saltiness (Parmesan), one for texture (Pecorino or Asiago). The four melt into a sauce that is more than the sum of its parts.
A good quattro formaggi avoids turning slimy – not too much sauce on the pasta, not too little. Often a fifth, secret cheese such as Grana Padano holds all the others together.