Baked donuts may turn out dense for several reasons. Avoid these for a more fluffy texture.  Over mixing. Make sure you're not to over-mixing. You want to mix everything until just combined.  Leavening Agents. Use double-acting baking powder. Regular baking powder, without “double-acting”, won’t work.  Fats. The heavy cream, unsalted butter, and egg yolks all have fats that help keep the donuts soft and fluffy instead of dense and dry. Don’t substitute too much. Over baked. Watch the time carefully and set an alarm to prevent over baking the donuts.