(12 servings)
Beat the butter until soft and foamy (3 to 5 minutes).
Add half of the powdered sugar and then the other half, beating well between both batches.
Then add the flour and salt in two batches, beating well between both batches.
Reduce the speed of the mixer and add the pistachios and blueberries chopped not too small.
Split the dough into two and place both parts on a piece of parchment paper or plastic wrap. Form a roll or a square and refrigerate for at least 1 hour, until firm.
Preheat the oven to 300°F and cut pieces of dough using a sharp knife. Place the cookies on a tray covered with parchment paper and put in the oven for about 15 minutes until the center is firm and the cookies are a bit brown.
Allow to cool completely on a baking rack.
