Preheat oven to 425°F. Spray donut pan with nonstick cooking spray.
In large mixing bowl, sift together cake flour, sugar, baking powder, nutmeg and salt. Add buttermilk, eggs and butter and beat until just combined. Fill each donut cup approximately 2/3 full.
Bake 7–8 minutes or until the top of the donuts spring back when touched (this is the timing for mini donuts. Not sure what the time is for full size ones). Let cool in pan for 4–5 minutes before removing. Finish donuts with chocolate ganache or vanilla glaze.