ground coffeeI bought mine from Trader Joe's, but you can use whatever kind you like
Preheat oven to 300F degrees. Make sure your oven is on the conventional setting. (or in other words, if your oven has a fan inside of it, avoid having the fan on).
Sift the almond flour and powdered sugar into a bowl and mix to combine. Sifting is crucial because you want to get rid of any larger pieces of almond.
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 sugar. Beat for another 4-5 minutes or until stiff peaks form.
Fold flour/sugar mixture into the egg white mixture. Be careful NOT to over mix. About 80 turns of your spatula should be enough. You want the batter to resemble the consistency of molten lava. I recommend using a large spatula. That way every turn will mix more of the flour into the egg whites.
Fill a pastry bag with the batter. Using a circle piping tip about 1/2 inch in diameter, pipe out 1 inch mounds. Make sure to pipe out onto parchment paper. Do not add any grease to the cookie sheets.
Take the cookie sheets and bang them onto the counter a few times to get rid of any air. I hit them pretty hard, about 10 times.
I like to sprinkle some coffee grounds on top of every mound to give it a stronger coffee taste, but that's totally optional.
Let the macarons sit in room temperature for about 30-50 minutes. It really depends on how quickly they become tacky to the touch. If you live in an area with a lot of humidity, it may take longer for the macarons to form the "skin".
Bake 1 tray at a time for 18 minutes. Be careful NOT to under bake or else they will stick to the parchment paper. I found that the second batch that sat out while the first was baking tended to burn a little since it sat out longer. So you may want to remove the second batch from the oven a minute or two earlier.
Heat the heavy cream in a saucepan over medium high heat until it comes to slight boil. Dump the the chocolate chips into a bowl and pour the hot cream over the chocolate making sure to submerge it. Let the chocolate sit for a few minutes then stir until it becomes a smooth creamy consistency.
Fill a disposable piping bag with the chocolate ganache and snip the tip with scissors.
Flip the cookies on their backs, and pipe a small mound of filling on one of them. Then place the other cookie on top.
If not eaten right away, store macrons in the refrigerator.