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A leftover dries out when you reheat it too hard and with nothing. The secret is a little moisture and a lid: a spoon of water and a plate on the bowl in the microwave, a splash of water and a lid in the pan, a sheet of foil over the dish in the oven. And you reheat until it is steaming all through, not just lukewarm.
Covered, with a spoon of water, and stirred halfway. That is true for the microwave as for the pan.
Three minutes in the microwave, five in the pan, twenty in the oven. Often less than cooking.
It is dry: a spoon of water, cream or sauce, a lid, one more minute. It is lukewarm in the centre and burning on the edges: that is the microwave, stir and put it back a minute on medium power. The rice is hard: a little water, lid on, and it turns tender again in the steam.
Yesterday's bolognese sauce, reheated on low heat with two spoons of water while the pasta cooks.