It's on page 668 of the Complete Tightwad Gazette. You just make a regular sourdough bread recipe, for two loaves' worth, but then you roll it out after the first rising and top it. Bake it for the same amount of time you would have baked the bread. It makes two round pizzas or one 9x13 pan (which is the way I do it because we like thick crust).

We like our cheese pretty brown, though. If you want to avoid the risk of burning the cheese, you should parbake the crust for about ten minutes, THEN top it, then bake the whole thing the rest of the way.