My husband and I happen to really like leeks. They're very mild and sweet compared to a standard onion. For this pizza, I paired leeks with mushrooms and prosciutto. I topped the pizza dough with shredded fontina and parmigiano reggiano cheeses, and then added sauteed leeks and mushrooms, along with prosciutto strips. I baked the pizza on a stone at 450 degrees for 15 minutes. The combination of sweet leeks, earthy mushrooms and salty prosciutto was a real winner. I just used regular button mushrooms, if you wanted you could try something a little more exotic.