Never again will you eat a soggy, microwaved piece of leftover pizza.
Reheated leftover pizza always pales in comparison with a freshly baked pie. The microwave turns it soggy, while throwing it into a hot oven can dry it out. We recently discovered a reheating method that really works: Place the cold slices on a rimmed baking sheet, cover the sheet tightly with aluminum foil, and place it on the lowest rack of a cold oven. Then set the oven temperature to 275 degrees and let the pizza warm for 25 to 30 minutes. This approach leaves the interior of the crust soft, the cheese melty, and the toppings and bottom hot and crisp but not dehydrated.
Why does this method work? Like other breads stored for a day, pizza crust initially hardens not through moisture loss but because its starches undergo a process called retrogradation, whereby the starch molecules crystallize and absorb moisture, making the pizza crust appear stiff and dry. As long as the pizza has been stored well wrapped, however, retrogradation can be temporarily reversed by reheating the pizza to at least 140 degrees—the temperature at which the starch crystals break down and release the trapped moisture, softening the crust. Placing the slices in a cold oven lets them warm up gradually, with ample time to release moisture and soften, while sealing the pan helps keep them from drying out as they reheat. Finally, placing the pan as low as possible in the oven means the slices are heated from the bottom up, so the underside of the crust crisps but the toppings don’t shrivel.