Preheat oven to 350 degrees Fahrenheit. Lightly butter a 9*13 baking dish. cook the spaghetti in a large pot of water until al dente. Drain well and spread it on a baking sheet; let cool.
In a large bowl toss the Fontina with the Mozzarella and Gruyere. Spread 1/3 of the spaghetti in the prepared baking dish in an even layer. Sprinkle 1/3 of the mixed cheeses and half the Gorgonzola over the spaghetti and season with salt and pepper. Repeat with another layer of spaghetti, mixed cheeses, Gorgonzola and salt and pepper. Top with the remaining spaghetti and cheeses.
Bake in the center of the oven until the top is golden brown, about 40 minutes. Let cool slightly before cutting into squares and serving.