- In a mixer bowl with a "Hook" attachment combine the buttermilk, water, yolks, flour and yeast. Mix for 3 minutes at a low speed.
- Add salt and sugar, and mix. Add the cold butter cut into cubes, and knead until the dough stops sticking to the walls (for 10-15 minutes).
- Shape a ball, place it in a clean bowl, cover with a towel, and leave for an hour in a warm place.
- Roll the dough 7mm (0.28 inch) thick. Cut out the circles about 6-8cm (2.35-3.15 inch) in diameter. Make a hole in the middle (if you wish). Cover the blanks with film, and leave for another hour.
- Pour the cooking oil into a pan for about 2-3cm (0.80-1.20 inch). Warm it until 320F (160C). Fry the donuts until golden crust for 1 minute on each side.
- Use a skimmer to take the finished donuts out of oil. Place them on a paper towel. Decorate with blueberry glaze (simply combine the juice with the powdered sugar until thickened).