Preheat oven to 375 degrees F (190 degrees C). Grease 12 muffin cups.
Mix 1 1/2 cup confectioners' sugar, almond meal, butter, flour, egg whites, and xanthan gum together in a bowl until just combined. The mixture will be slightly grainy. Spoon batter into prepared muffin cups. Scatter blueberries onto batter.
Bake in the preheated oven until a toothpick inserted in the center of a muffin comes out clean, about 25 minutes. Cool muffins in pan for 10 minutes before transferring to a wire rack. Dust with about 2 tablespoons confectioners' sugar.