Sift all the dry ingredients together.
In a separate jug, combine the butter, oil, sugar, eggs, vanilla, sour cream and buttermilk.
Add the wet ingredients to the flour and mix to combine. The batter should be smooth and lump-free.
Spray a mini waffle maker with non-stick cooking spray. Ladle 1 tablespoon of batter into each donut hole and cook for several minutes.
Alternatively, if using a donut pan, bake in a preheated oven at 180º C for about 15-18 minutes or until cooked through.
Transfer the cooked donuts to a cooling rack and continue with the remaining batter.
To make the glaze, combine the powdered sugar, milk and salt in a small mixing bowl.
Once completely cool, dip the tops of the donuts into the glaze and allow excess to drip off.
Scatter with crystal sugar beads if desired and set aside until the glaze is firm and dry.