Preheat oven to 350ºF (180ºC).
Line two baking sheets with parchment paper and have a pastry bag with a plain tip (about 1/2-inch, 1cm) ready.
Grind together the powdered sugar with the almond powder and cocoa so there are no lumps; use a blender or food processor. Then sift the mixture into a large bowl and discard the larger lumps.
Using a mixer beat the egg whites until they begin to rise and hold their shape. While whipping, beat in the granulated sugar until very stiff and firm, about 2 minutes.
Fold the dry ingredients, in two batches, into the beaten egg whites with a rubber spatula. When the mixture is smooth and there are no streaks of egg white, stop folding and scrape the batter into the pastry bag. (standing the bag in a tall glass helps if you’re alone).
Pipe the batter on the parchment-lined baking sheets in 1-inch (2.5 cm) circles evenly spaced one-inch (2.5cm) apart.
Rap the baking sheet a few times firmly on the counter top to flatten the macarons, and remove air bubbles. Allow the macarons to sit for 20 to 30 minutes until a “skin” forms and they are no longer wet when lightly touched.
Bake them for 10-15 minutes. Let cool completely then remove from baking sheet.
To make the chocolate filling: in a small saucepan heat the cream and instant coffee if used. When the cream just begins to boil at the edges, remove from heat and pour over the chopped chocolate. Let sit one minute, then stir until smooth. Stir in the butter. Let cool completely before using.
Spread a bit of batter on the inside of the macarons then sandwich them together.
Let them stand at least one day before serving, to meld the flavors. Serve macarons at room temperature.