While cold pizza in itself is a treat, warmed-up pizza fresh from the oven has a just-cooked crispness that’s difficult to resist, especially when compared to the too-chewy or overly soggy pizza crust that can result from microwave heating. But heating up leftover pizza can be tricky: give it too little oven heat for too long and you risk sitting down to dried-out, crunchy crust. Turn the oven heat up too high, and you may burn the cheese. Exact cooking time varies, depending upon the thickness of your pizza crust, so ensure pizza-heating success by monitoring the pizza closely as it heats up.
Heat up leftover pizza with a pizza stone, which helps produce a crisp crust by absorbing excess oil and moisture. Put the pizza stone on the center of the bottom oven rack, then turn the oven on to 400 degrees Fahrenheit and allow the stone to preheat completely, which typically takes 30 minutes or more. Leave the oven on and transfer the pizza slices to the heated pizza stone, exercising care not to burn your hands during the process. Leave the pizza slices to heat up on the pizza stone for six to 10 minutes, or until the cheese on the top of the pizza is bubbly and melted.
Warm up your pizza in the oven on a baking sheet. Line the baking sheet with parchment paper to ensure a crisp, non-soggy crust, and put the pan in the oven to preheat at 350 degrees Fahrenheit for 10 to 15 minutes. Set the slices of cold pizza directly on the parchment paper-covered baking sheet and leave them in the oven to heat for 5 to 8 minutes, or until the crust is crispy and the cheese bubbles slightly. Leave the oven turned on throughout the duration of the pizza warm-up time.
Substitute a sheet of aluminum foil for a baking sheet if you’d prefer not to use a pan. Preheat the oven to 400 degrees Fahrenheit and bake the pizza for 8 to 10 minutes, leaving the oven turned on until you've completely heated and removed the pizza.