Instructions

1. Preheat the oven to 350 degrees F (177 degrees C). Spray donut pans with nonstick cooking spray and set aside
2. Prepare Donut Batter: In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter, sugar, salt, and vanilla until light and fluffy, about 3 minutes. In a separate bowl, whisk together the all-purpose and cake flours, baking soda, and baking powder. Add the whole eggs and egg yolk to the mixer and cream until blended, about 1 minute, stopping to scrape the sides as needed. Alternately add the flour mixture and the buttermilk in 3 stages, mixing on medium-low and stopping to scrape down the sides between additions. Turn mixer to low and gently stir in the blueberries, mixing just until evenly incorporated and the batter is a nice shade of blue/purple
3. Bake Donuts: Fill a large piping bag (or large ziplock bag with a corner cut off) with the batter. Pipe batter into each donut well until each is about ⅔ of the way full (do not fill to the top). Bake in preheated oven for 18 to 20 minutes or until the donuts spring back when poked. Allow to cool completely before glazing
4. Prepare the Glaze: In a big bowl, combine all the ingredients and whisk together. Adjust the consistency by adding either milk to thin one teaspoon at a time or powdered sugar to thicken one tablespoon at a time
5. Dip Donuts: Once donuts are completely cool, dip each donut top and bottom into the glaze, shaking off any excess, and placing on a wire rack set over a baking sheet lined with parchment paper