Sift the flour, 39 g deZaan Holland Carbon Black 10/12% Dutched Cocoa Powder, baking powder, and salt together. Set aside.
Cream the butter and granulated sugar until light and fluffy.
Add in the egg and vanilla. Mix to combine. Add in the dry ingredients and mix on low until just combined. Do not over-mix.
Divide the dough in two. Roll each portion between two pieces of parchment to 0.6 cm/0.25 inch thickness.
Cut the dough into desired shape and size. Chill the sheets until firm. This will make it easy to separate the pieces.
Lay out the cookies onto parchment-lined sheet trays. Space them about 2.5 cm/1 inch apart.
Bake at 176°C/350°F for about 12-15 minutes.
To make the filling, combine all of the ingredients in the bowl of a stand mixer. With a paddle, cream until smooth.
Roll the batter out between two pieces of parchment to 0.6 cm/0.25 inch thickness and freeze.
Once firm, cut the filling to the same size as the cookies. Place the filling in between two pieces of the cookies.