In a heavy-bottomed large pot or deep fryer, heat at least 2 inches of oil until a deep-fry thermometer registers 350°F. Working in batches, use a slotted metal spoon or spatula to carefully place the donuts into the hot oil. Fry, flipping once, until light golden brown, 1 to 2 minutes per side. When done, transfer to a wire rack. Make sure to return the oil to 350°F between batches.