Preheat the oven to 350° F. Spray donut molds with nonstick spray and set aside.
In a large bowl, whisk together the flour, sugar, baking powder, and salt
In a medium bowl, whisk together the egg, buttermilk, melted butter, and vanilla. Pour this mixture into the dry ingredients, and mix until just combined.
Scoop this mixture into a piping/ziploc bag to pipe into the donut pan and fill the donut pan ½ full with batter. If you are using silicone donut molds, place them on a baking sheet before putting them into the oven.
Bake for 9-12 minutes or until set on top. Transfer the donut pan to a wire rack and allow the donuts to cool for about 5 minutes. Carefully take the donuts out of the pan and allow them to cool completely on the wire cooling rack before icing.
Strawberry Glaze
Add the fresh strawberries to a blender or food processor and blend until smooth. Pour this into a bowl.
Add the 1 cup of powdered sugar and mix until smooth. If the icing is too thick, add in up to ½ tablespoon of milk. If it is too thin, add powdered sugar.
Notes
To make homemade buttermilk, pour ½ tablespoon of white vinegar or lemon juice into a liquid measuring cup. Fill the measuring cup to the ½-cup mark with milk. Allow the mixture to sit for 5-10 minutes. This allows the mixture to curdle like buttermilk.
Use a scale to measure your flour properly.
Make sure not to overfill the donut pan! If you fill it up more than ½ way full it might overflow while baking.
Only dip the donuts in glaze once they’re completely cool, otherwise, the strawberry glaze might melt right off.