Sift the flour with the baking powder onto a floured surface and make a well in the middle of the flour. Pour the sugars into the well and make another well with a spoon.
Break the egg into the well and mix the eggs and sugar together. Slowly mix in a small amount of flour from the rim to make a thick creamy mixture in the well.
Lay the butter pieces on top of the cream mixture and top with flour from the outside bottom of the mound by scraping the flour up the sides.
Knead the dough until it is no longer sticky but glossy and pliable (keep extra flour on hand to keep your dough from being too sticky)
Dissolve the cocoa powder into the milk. Cut the dough in half and blend the cocoa mixture into one of the halves.
Roll the halves into logs and wrap them both in plastic wrap. Store in the fridge for a few hours.
Preheat oven to 350 degrees F.
Spray two large baking sheets with spray and set aside.
Lightly flour a rolling pin and a flat surface. Then roll each half of dough into 12x10 rectangles. Then lift the black sheet of dough and set it on the white one. Hand roll them into a jelly-roll starting at the long end.
With a sharp knife, cut into half inch slices and place on the baking sheet. Bake until golden brown (12-15 min). Remove and let cool on a rack.