Mix the dry ingredients in a bowl: flour, baking powder and powdered sugar.
Separately, mix the yolks and egg whites and whisk with a fork until well mixed.
Preheat the oven to 360°F.
Add the beaten egg, vanilla extract and cold melted butter to the dry ingredients. Mix and add blueberries.
Separate in 8 equal parts and shape them.
Place on a buttered tray or a silicone mat. Flatten them and make a cross over each bread with a knife.
Brush with egg glaze and bake for 15 minutes or until brown. Allow to cool before serving.