Get ahead! You can make the mashed potato mixture up to 2 days ahead; cover and refrigerate. You can bake the crust up to 8 hours ahead: Let it cool, then loosely wrap the whole baking sheet in plastic. (If you need only one pizza, wrap half of the unbaked dough in plastic and freeze up to 1 month. Thaw in the refrigerator overnight, let rest for 4 hours at room temperature and drizzle with olive oil before stretching.)