Preheat oven to 350ᵒ F. at least 20 minutes before making this recipe.
Combine milk with lemon juice in a sealed container and allow to sit in the refrigerator. The mixture will curdle slightly. Meanwhile, combine dry ingredients in a large mixing bowl: wheat flour, cake flour, sugar, baking powder, baking soda, cardamom, and lemon zest. Mix until well combined.
Once buttermilk mixture has sat for 20 minutes, remove from fridge.
In a separate bowl, combine wet ingredients: buttermilk mixture, melted butter, egg. Blend well. Slowly add wet ingredients to dry ingredients until well combined, then fold in finely chopped blueberries and mix well. Spoon mixture into a large pastry bag or 1 gallon sealed plastic ziplock bag with a corner cut off and fill pre-greased donut baking pans each about ¾ of the way. Bake donuts for approximately 10 minutes at 350ᵒ F., or until lightly brown. Remove from oven and allow to cool slightly on a baking rack.
Meanwhile, fill deep frying pot with vegetable oil to about 2” deep.
Heat oil to approximately 365ᵒ F. Fry each donut in oil for about 20–30 seconds on each side or until medium brown color appears. Allow grease to drain from donuts and for them to cool slightly.
While donuts are cooling, place ½ cup chopped blueberries and a ½ cup of water in a sauté pan on medium heat. Bring mixture to a slight boil and cook blueberries down until completely soft. Remove from heat and combine with powdered sugar and milk in a medium bowl until desired icing thickness has been reached.
When donuts are cooled to the touch, dip the top of donuts into icing mixture and drip dry on a baking rack. Allow icing to harden slightly then serve.
Makes approximately 1 dozen donuts.
Serving Size 1