Preheat your oven to 350 degrees F (175 C). Grease two 6-cavity donut pans (this recipe makes 12 donuts). If using a muffin pan, spray with baking spray or use baking cups.
In a bowl, combine the dry ingredients: flour, 1 1/2 cups granulated sugar, and baking powder. Set aside.
In a separate bowl, whisk together the egg, whole milk, and melted butter. Add vanilla extract, 2 tbsp lemon juice, lemon extract, and lemon zest, whisking until combined.
Pour the wet ingredients into the dry ingredients and mix until just combined. You can use a whisk, stand mixer, or handheld mixer. Add 1 cup of blueberries and gently fold them into the batter with a spatula.
Pipe or spoon the donut mix into the donut pans, filling each cavity about 3/4 of the way. Bake for 10-12 minutes.
Cool the donuts in the pan for 5 minutes, then carefully pop them out onto a cooling rack.
While the donuts are cooling, prepare the glaze. Combine 3 tbsp lemon juice and the blended blueberries and blackberries in a blender. Blend on high speed until you have a smooth liquid. In a bowl, combine the berry juice with 1 cup powder sugar and stir until smooth. Add 0.5 lemon's worth of lemon zest and give one final stir.
Once the donuts have cooled slightly, you can roll their sides in the 1/3 cup granulated sugar (optional) before glazing.
Finally, dip or drizzle the cooled donuts with the berry glaze. Enjoy!
