Remove the peel off the grapefruit. Try to remove it in as few pieces as possible. It should be about ⅛ of an inch in thickness. Cut the peel into thing slices about ¼ inch wide. Boil the peel in a small saucepan for about 5 minutes. Drain and boil again for another 5 minutes, or until the peel begins to look translucent. Drain well. Toss in the sugar and leave on a wire rack to cool and harden. When ready to use, dice roughly.

Beat the butter until smooth. Add the sugar and chili peppers and mix until light and fluffy. Add the eggs, one at a time, waiting until the last one is completely incorporated before adding the next. Add in the vanilla and grapefruit.

In a bowl, mix together the flour, cocoa powder, and baking powder. Slowly add to the wet ingredients and mix until it is just incorporated. Drizzle in the melted chocolate and mix until it is fully incorporated without over mixing. Fold in the diced grapefruit peel.

Lightly butter the madeleine pans and coat with a thin layer of cocoa powder. Fill the cavities and bake for 8 - 10 minutes. Remove from the pan and sprinkle powdered sugar over the cookies.