Reheating Frozen Leftover Pizza

This will not restore leftover frozen pizza to the way it tasted while fresh....

My first rule of leftovers (I'm very very good with leftovers; as a food critic, I've had to cope with a fridge perennially full of greasy brown paper bags) is: don't try to recreate the original meal. Just find some way to make it delicious. If you aim to recreate the original meal, you will 1. fail, and 2. work within a low ceiling of possible quality, which is why everyone normally hates leftovers. I view leftovers as mere fodder to be disrespectfully repurposed, retrofitted, and recycled rather than resurrected.

...but it will result in something tasty and worth eating.

I assume you've wrapped the frozen slices individually in tight aluminum foil. If that's not true, improve your procedure, fast forward, then proceed.

Open the foil to expose the top surface of the slice. Place it directly on the rack your toaster oven at 350 degrees (preheating's unnecessary). Check frequently after four minutes. When the cheese begins to just barely loosen (not warm but not fully frozen), heat a cast iron skillet or griddle on medium. A couple minutes later, transfer slice (still encased in foil, which should now be lightly re-closed) from the toaster oven to the skillet/griddle. After three minutes, watch carefully, as the crust can suddenly burn right through the aluminum (I'd suggest, btw, using thick heavy-duty aluminum, which also offers better freezer protection).

When the kitchen smells like pizza, and the crust's underside is beginning to pick up some additional color (perhaps there are minor dark (not black) patches appearing; that's ok...again, we're not recreating the original experience), serve. Note that while crust will be hot, the cheese will be pleasantly warm, not hot. If you want the whole thing raging hot, you'll be forced to eat a dried-out cracker with unpleasantly molten twice-cooked cheese. Ick.

If the slice has significant toppings, and they're not quite warm, open up the top foil and pop the slice back into toaster oven at high temperature (broil, if possible) for just a short time...and watch it like a hawk. Do not wait till cheese bubbles or top crust begins to brown! That's much too late! This isn’t like the original baking of the pizza (again: don’t try to recreate).


Further Reading:
A Toasted Bagel Tutorial and Manifesto