Preheat the oven to 350F

Combine the flour, cocoa powder, baking powder and salt and then sift it.

Cream the butter and sugar together on high speed until light and fluffy. Should take a few minutes. I used the whisk attachment.

Beat the egg separately and mix it with the butter and sugar using medium speed.

Change the attachment to the paddle attachment.

Slowly add it in the flour mixture until well combined.

Remove the dough from the mixture, wrap it plastic wrap and chill it for at least 2 hours.

Roll out the dough and cut out your cookie shapes. Make sure to do half the cookies with a solid shape for the bottom and half the cookies with a window for the top.

Bake the cookies for about 12-15 mins (depending on your oven)

After it's done, let them cool to room temperature

To assemble: flip the solid cookie upside down and place a dollop of jam on it. Take a window cookie and place some jam at the bottom as a glue. Press the top and bottom together.