1Preheat the oven to 450°F and arrange a rack in the middle.
2Divide the pizza dough into 2 balls and roll them out to 1/4 inch thick. Transfer to 2 baking sheets.
3Spread the crushed tomatoes evenly on the dough. Distribute the fontina, mozzarella slices, crumbled Gorgonzola, and onion slices evenly over the pizzas.
4Bake the first pizza until the underside of the crust is golden brown, about 15 minutes. Remove from the oven and immediately brush the crust with a little olive oil (this gives it a nice sheen and a bit of extra flavor). Sprinkle with half the Parmesan and serve while hot. Repeat with the second pizza.