Pierogi (East European origin) are a dumpling stuffed with mashed potato and cheese then cooked in boiling water and served with bacon, sautéed mushrooms, and caramelized onions. Served with sour cream on the side.
Remove lid from tray and cover with napkin or paper towel. Warm in microwave or reheat in frying pan, stir often. You can also use a casserole dish with lid and warm in oven at 350F for 20 minutes.