While Italy, and more precisely Naples, is pizza's spiritual home, it's fair to say it has become one of the world's favourite foods. Pizza comes in many styles - round, square, a metre or more in length, thin, thick, filled, fried or sweet, with a crust that's high or low, soft or crunchy. And the quality of the pizza is defined by the quality of the flour, the dough and the ingredients for the topping.