METHOD:

1. Place the sugar and melted butter in a large bowl and combine with a whisk until smooth.
2. Add the egg, oil, and vanilla and whisk until combined.
3. In a separate medium bowl, add the flour, baking powder, bicarbonate of soda, nutmeg, and salt. Mix to gently combine.
4. Add half the dry mixture into the wet mixture, whisk gently until some of the flour remains, then add all the buttermilk, mix a little, and add the rest of the flour. Mix until just combined, do not overmix. The batter will be very wet and there will be a few lumps. 
5. Transfer the batter to a piping bag or a plastic bag with a corner cut off. (You can also just use a spoon and smooth out the top.)
6. Grease a doughnut tray with cooking spray and fill each cavity ½ to ¾ of the way full of batter. 
7. Bake at 235ºC for 7-9 minutes. When the tops are firm and bounce back when you touch them, they're done. 
8. Cool the doughnuts in the pan for 5 minutes, then flip them out onto a wire rack to cool completely. Make sure to not glaze while warm.

For The Glaze

1. Sift your icing sugar, this will prevent your glaze from having lumps.
2. In a medium bowl, whisk together icing sugar and water (or milk) until desired consistency. Add ¼ teaspoon more water at a time until it's as thin as you like. If it becomes too thin, add more icing sugar. If your glaze has lumps, you can use a hand mixer to smooth it out. 
3. If you want a more opaque glaze, add a few drops of white food colouring to the glaze and divide into bowls. Add your favourite colours and stir. 
4. Place the wire rack of doughnuts on top of a sheet pan to catch extra glaze drips. Grasp each doughnut by the sides and dunk into the glaze, letting it drain off for a few seconds. Then flip over and place the doughnut back onto the wire rack. Top with sprinkles immediately, as the glaze firms up quickly.