White pizza, or pizza bianca, is one of my favorite varieties of pizza. Like other red pizzas, its construction and the cheeses used vary regionally. One of the tastiest, I think, uses ricotta as one of the cheeses, but not many do. Some white pizzas are adorned with broccoli florets or less commonly, spinach.
White pizza is actually very easy to make at home and a nice change from the tomato-laden variety. Start with any type of pizza dough - homemade, store-bought or even a prepared shell from the supermarket. Brush the shell with extra-virgin olive oil and dust with ground rosemary and oregano. Sprinkle generously with grated mozzarella. You can also employ other cheeses as well - romano and parmesan work nicely on a white pizza. Then top with dollops of riccotta about two inches apart.
Another method is to spread the riccotta and then cover it with the mozzarella and other cheeses, it's up to you. You can spice it up with diced onion and fresh garlic sprinkled on top. Fold your dough over and it makes a wonderful calzone.
If you simply can't do without your tomatoes, sun-dried tomatoes are another option for a topping, but I prefer my white pizza to be rich in cheese and garlic. Bake until the cheese is bubbly and the crust is golden brown.