Unsalted butter, for greasing 1 1/2 pounds spaghetti  Kosher salt and freshly ground black pepper  8 ounces imported fontina cheese, coarsely shredded (2 cups)  8 ounces Gruyere, coarsely shredded (2 cups)  8 ounces mozzarella, coarsely shredded (2 cups)  4 ounces Gorgonzola dolce, crumbled  Preheat the oven to 350 degrees F. Lightly butter a 9-by-13-inch baking…