Nutella donuts are best enjoyed the same day they are made. They are fresh and light and have the best texture. If you have leftovers, store them in an airtight container at room temperature for up to 2 days. Sometimes as the doughnuts sit, they start to get stale, making them have a dense texture. Reheat in the microwave for about 15 seconds and the doughnut becomes soft again. Be careful that the filing has not gotten too warm. It can cause a burn. Once the doughnut is cool enough, enjoy.