Preheat oven to 400°F.
Sift together the flour, baking powder and salt.
Place butter and cream cheese into the bowl with the flour mixture and cut together until fully incorporated. The mixture should be evenly grainy.
Add water and vinegar and knead together until the mixture comes together and a smooth dough forms, about 2 minutes.
Pat the dough into a disc, cover with plastic wrap and chill in the refrigerator for about 30 minutes.
Place the ingredients for the filling into a mixing bowl and gently stir together until well combined and the blueberries are well coated.
Once the dough has chilled, place it onto a lightly floured surface and roll out until ¼ inch thick. Using a 2 ½ to 3 inch circle cutter cut out as many circles possible, about 14.
Re-roll the scraps and make more circles.
Whisk together the egg and water and brush a thin layer over each disc. Place 2 teaspoons of the filling into the center of each disc of dough and fold the sides towards the center, until all the sides have been tucked in.
Brush the tops of the dough with egg wash and sprinkle with a small amount of sugar.
Place the mini galettes onto a baking sheet, lined with parchment, and bake for 11 to 13 minutes or until golden brown.
Allow the glaettes to cool slightly before serving.