In a deep bowl, whisk the butter and sugar together. Add the eggs one by one, whisking between each addition. Add the vanilla extract, instant coffee, melted chocolate and mix until the whole mixture is combined. In a deep bowl, mix the flour, baking powder, salt and cocoa until combined. Gradually add the dry ingredients to the liquid ones while mixing to combine the two mixtures. Pour the mixture into a greased pan. Bake the cubes for about 25 minutes to 30 minutes at 180 degrees. Cool completely and cut into rectangles. With the help of the glaze, decorate the reindeer as in the photo.