Preheat your oven to 350°F (175°C) and grease a mini donut pan.
In a mixing bowl, combine flour, sugar, baking powder, baking soda, and salt.
In another bowl, whisk together buttermilk, egg, melted butter, and vanilla extract.
Gradually add the wet ingredients to the dry ingredients, mixing until just combined.
Transfer the batter to a piping bag or a zip-top bag with a corner snipped off.
Pipe the batter into the mini donut pan, filling each cavity about halfway.
Bake for 5-7 minutes, or until the donuts spring back when touched.
Allow the donuts to cool in the pan for a few minutes before transferring to a wire rack.
Once cooled, decorate with icing and sprinkles as desired.
Enjoy your homemade mini donuts fresh!