Preheat the oven to 350 ˚F. In a bowl mix almond flour, erythritol, baking powder, and salt. Add the butter and mix again until you obtain a smooth mixture. Add the frozen blueberries and gently mix it into the dough. Form small balls with 2 tbsp of dough and place them on a baking sheet. Gently press down the ball with your hand; you can wet your hand if the dough is too sticky. Place in the oven and bake for 15 minutes. Remove from the oven and let it cool for 20 minutes. During that time, in a small bowl, mix the sugar-free powdered sugar with the coconut milk. Once the cookies are cool, pour the sugar mixture on top with a spoon.