Mix the flour, cocoa powder, baking powder and salt together.

In a separate bowl, beat the butter and sugar until light and fluffy.

Beat in the egg and vanilla extract until combined.

Beat in the flour mixture a little bit at a time.

Divide the dough in half and with each half roll into a 9 inch long and 2 inch in diameter log. Wrap in plastic wrap and freeze for 15 minutes or until firm. Note: You can also stick in the fridge for 1 hour or until firm.

Preheat the oven to 350°F. Line two baking sheets with parchment paper or a silpat mat.

Cut the logs into 1/4 inch cookies. Bake for 10 minutes or until set.

Allow the cookies to cool for 3 minutes on the cookie sheet before transferring to a cooling rack to cool completely.

Beat the ingredients together and place into a piping bag.

Squeeze a dollop on one cookie and top with another cookie.