This is a dish that just doesn’t reheat well, so I suggest making only as much as you can eat in one serving. That said, I prefer not to waste food, so if you have any leftovers, I find the best way to reheat carbonara is to add about 2 teaspoons of water to the dish and microwave in 30 second increments, stirring in between, until it's warmed through. Don't let it get too hot or the eggs will scramble.