Preheat oven to 375 degrees F (190 degrees C). Butter one Madeleine pan.
Sift the flour, cocoa, baking powder and salt together. Set aside.
Cream the butter with the vanilla and the sugar. Add the egg and egg yolks, beating to mix. Stir in the dry ingredients until just combined only, do not over mix. Place rounded teaspoon of batter into the prepared Madeleine shell forms.
Bake at 375 degrees F (190 degrees C) for 12 minutes. Remove from oven and immediately invert onto a wire rack to cool. Once cool sprinkle with confectioners' sugar, if desired.