In the bowl of your stand mixer, mix together flour, sugar, baking powder and salt.
Add buttermilk, egg, and butter, and mix until JUST combined.
Pour batter into a piping bag or ziplock with the corner cut out, and fill each donut cup 1/2 full. Don't get crazy about this - the batter will rise quite a bit during baking, and you do want holes! (Overfilling just makes the hole close up)
Bake 6 minutes or until the top of the donut springs back when touched.
Cool in pan for 1-2 minutes, then transfer to a cooling rack.
Glaze (either flavor)
Combine all ingredients and mix until sugar is dissolved. Mixture will be runny.
Dip cooled donuts in and set on cooling rack for 5-10 minutes.
Re-dip and sprinkle your chosen decorations on top, and let dry.