Pre heat oven to 190°C/375°F and spray donut pan with cooking spray
In a mixing bowl, combine the flour, baking powder, baking soda and salt, then set aside.
In a jug, combine the milk and lemon juice (it will look curdled). Set aside
In the bowl of a stand mixer, beat the butter and sugar on medium speed until light and fluffy (approx 2 minutes)
Scrape the bowl with a spatula, then add the egg and vanilla. Beat again until well combined (approx 1 minute)
With the mixer on low, add ⅓ of the flour mixture, then ½ of the milk mixture, repeating until you finish with the last ⅓ of flour mixture. Mix until only just combined.
Scoop batter into a piping bag or snap lock back, then cut the end of the bag and pipe batter into the donut pan, filling the holes halfway.
Bake donuts for 10 minutes or until a skewer comes out clean
Cool for 5 minutes, then flip the pan onto a cooling rack to cool completely before dipping into the glaze