Sift Ingredients: Sift the almond flour and powdered sugar into a bowl using a fine-mesh sieve and mix to combine. Set aside.
Beat Egg Whites: Beat the egg whites on high speed until foamy, then add espresso powder, salt, and cream of tartar. Mix for another minute, then add the granulated sugar. Beat for another 4-5 minutes or until stiff peaks form.
Combine Mixtures: Fold the flour/sugar mixture into the egg white mixture. Be careful NOT to overmix. About 80 turns of your spatula should be enough, aiming for a consistency resembling molten lava.
Pipe Batter: Fill a pastry bag with the batter. Using a Wilton 1A piping tip, pipe out 1-inch mounds onto parchment paper. Bang the cookie sheets on the counter a few times to release air bubbles. Optionally, sprinkle some coffee grounds on top of each mound.
Rest and Bake: Let the macarons sit at room temperature for about 30-50 minutes until tacky to the touch. Preheat oven to 300°F (150°C) on a conventional setting. Bake one tray at a time for 18 minutes. Adjust time for subsequent batches as necessary.
Prepare Ganache: Heat the heavy cream in a saucepan over medium-high heat until it comes to a slight boil. Pour over chocolate chips in a bowl, ensuring they are submerged. Let sit for a few minutes, then stir until smooth.
Assemble Macarons: Fill a disposable piping bag with the chocolate ganache. Flip the cookies on their backs, pipe a small mound of filling on one, then place another cookie on top.