• Sift together the cocoa powder, flour, baking powder, salt in a large bowl, and set aside
• In a large mixing bowl, cream the butter, sugar and brown sugar. Add the egg & yolk one at a time, then the vanilla, followed by the instant coffee, mixing in each ingredient before adding the next.
• Add the dry ingredients and mix until incorporated.
• Divide the dough into 2 pieces, wrap with plastic wrap and cool in the refrigerator at least 1 hour.
• Knead the dough slightly to help soften and avoid cracks when rolling.
• Place one piece between 2 lightly floured sheets of parchment paper and roll into a 1⁄4-inch-thick rectangle. Repeat with the other piece of dough.
• Using a 2 inch round cookie cutter, cut the dough into about 64 circles. Any scraps will have to be re-chilled before you can re-roll it.
• Place the cookies about 2 inches apart on ungreased baking sheets and chill for 20 minutes.
• Preheat the oven to 325f/165c.
• Bake the cookies until they are set (about 8-10 minutes) be sure not to let them get too dark or the cookie will become bitter.
• Cool completely on cooling racks.

For the Filling:

• Roll out the fondant, using icing sugar for rolling (not flour) to just over a quarter of an inch thickness and cut into circles using the same cookie cutter as for the cookies.
• Brush one side of the fondant with a little milk and press this onto the bottom of one cookie.
• Brush the other side of the fondant with a little water and place the bottom of a second cookie, pressing gently to secure the sandwich.
• Repeat with the remaining cookies, re-rolling the fondant if needed.