1. Spray a doughnut pan with cooking oil and set aside.
2. In a large bowl, whisk together the flour, sugar, baking powder and salt.
3. In a small bowl, whisk together egg, milk, butter and vanilla extract.
4. Add the wet ingredients to the dry ingredients and stir together until no flour bits remain and all the ingredients are well combined. Do not overmix the batter.
5. Spoon the batter into 6 doughnut cavities.
6. Place the pan into a 350ºF oven and bake 8 to 10 minutes.
7. Remove from the oven and transfer to a wire rack to cool.
8. In a shallow bowl whisk together icing sugar, vanilla extract and salt. Add 1 Tbsp of milk and whisk to combine. Add additional milk, ½ tsp at a time, until glaze is desired consistency. Add food colouring if you wish.
9. Dip the warm doughnuts into the glaze and return to wire rack. Top with sprinkles if desired. Allow glaze to set for 30 minutes.