Preparation Steps

• In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla extract.
• In a separate bowl, whisk together the flour, baking powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Divide the dough in half.
• In a small bowl, combine the cocoa powder, milk, and powdered sugar to create a chocolate paste. Mix until smooth.
• On a lightly floured surface, roll out one half of the dough into a 12x9 inch rectangle. Spread the chocolate paste evenly over the dough. Roll out the other half of the dough to the same size and place it on top of the chocolate layer.
• Starting from one long side, tightly roll up the dough into a log. Wrap the log in plastic wrap and chill for at least 2 hours.
• Preheat oven to 375°F (190°C). Line baking sheets with parchment paper. Cut the chilled dough log into 0.25 inch thick slices.
• Place the cookies on the prepared baking sheets and bake for 10-12 minutes, or until the edges are lightly golden brown. Let cool on the baking sheets for a few minutes before transferring to a wire rack to cool completely.