Preheat the oven to 400F. Grease a doughnut pan, and set aside.
Whisk together the flour, baking powder, and salt. Set aside.
Whisk together the egg and sugar until combined. Add the buttermilk, oil, and vanilla, and whisk until combined.
Add the dry ingredients, and mix until just combined. Do not overmix. Fold in the strawberries.
Spoon the batter into the prepared doughnut pan, filling almost to the top. Bake for 10 - 12 minutes or until a toothpick inserted comes out clean.
Allow to cool for 5 - 10 minutes before transferring them to a wire rack to cool completely.
For the Glaze
Puree the chopped strawberries until smooth with a few tiny bits. Add the vanilla, and icing sugar, and mix until combined. Add milk, 1 tablespoon at a time, until the glaze is at your desired thickness.
Dip each doughnut into the glaze, and leave to set on the wire rack.
Notes
From: Marsha's Baking AddictionTo make your own buttermilk, simply add 1/2 tablespoon of fresh lemon juice or white vinegar to 1/2 cup (120ml) of milk. Stir to combine, and allow to sit for 5 - 10 minutes until slightly thickened and curdled.Leftover doughnuts can be stored in an airtight container at room temperature or in the fridge for up to 2 days. They also freeze well for up to 2 months. Thaw overnight in the fridge before serving.