300 grams unsalted butter
150 grams powdered sugar
1/2 teaspoon salt
400 grams flour
40 grams chocolate powder
2 egg whites
In mixing bowl, cream together unsalted butter and powdered until light and fluffy. Reserve half the mixture in one mixing bowl. This will remain your “white” dough. To one half, add in the chocolate powder. Divide the flour and salt. Mix in the salt and the flour to each bowl. Wrap in plastic wrap and chill in refrigerator for 2-3 hours or until hard enough to roll out.
Separate the eggs, discarding the yolks or saving for another purpose. Split the chocolate dough into 2 balls and repeat with the plain dough. Roll out one of the chocolate into a 1/4 inch thick surface; repeat with the vanilla dough (Note that I do this on parchment paper as you will need to left the entire dough surface in one piece). Cut to even sized rectangles.
Brush the dough with egg white (to use as glue) and then lay the vanilla dough flush on top of the chocolate dough. Smooth out any air bubbles that may have occurred. Next, carefully roll the dough into a log (this will create the pinwheel effect. Be as firm as you can as you don’t want to create any air pockets. Once firmly rolled, shape your heart. Using a long ruler, push in one side of the roll to a distinct line. Using your hands, gently manipulate the opposite end to a point. Looking at it from one end or the other of the log, it should have a distinct heart shape. Wrap in aluminum foil and chill in refrigerator for 2-3 hours. Repeat with remaining dough (you should have two heart rolls).
Preheat over to 400F. Unwrap chilled dough. Slice with sharp knife into 1/4 inch thick slices. Place on cookie sheet lined with silpat or onto parchment paper.
Bake 12-14 minutes or until golden brown at the edges. Cool on wire rack.