Preheat oven to 425 F.
Spray the donut pan with non-stick spray.
In large bowl, whisk the flour, sugar, baking powder, salt and nutmeg.
Stir in the the buttermilk, egg and butter until just combined. The dough will be slightly sticky and thick.
Place a slightly heaping tablespoon of dough into each donut cavity. Spread it out evenly with your finger to fill the circle.
Bake 6-7 minutes or until donut tops are spongy. Cool in pan for 3 minutes then transfer to cooling racks. Apply glaze only after donuts have cooled completely.