Trying to decide whether to simply dispose of some old, unused, naturally leavened pizza dough or to incorporate it into my starter, I chose option three: adding the old dough to a yeasted pizza crust.
You don't need dmcavanagh to tell you that slow-rise dough has a superior taste; the difference in flavor is evident from the first bite. As dough ferments, yeast converts starches to sugars, building a complex flavor and priming the crust for caramelization. By adding mature dough to the usual suspects (flour, water, salt, and yeast), however, you can achieve similar results relatively quickly.
After a few hours of rising, I had a wonderfully puffy and elastic dough that baked to a beautiful golden brown. Both the old dough and the spelt flour I had used contributed a rustic, country flavor that I hadn't yet achieved in any yeasted dough.
If you plan ahead, you can make this dough with a longer rise by reducing the ambient ferment to a half hour and refrigerating the dough at least overnight. Either way, this crust is reliable and delicious.
I topped the pizza with two of my favorite vegetables: mushrooms and summer squash. Mushroom pizza often becomes soggy as the crust absorbs water exuded by the mushrooms; I avoid this problem by pan-roasting the mushrooms before putting them on the pizza. This method has the added benefit of caramelizing the mushrooms beautifully. For summer squash pizza, the key is to slice the squash very thinly so it melts into the crust and caramelizes slightly.