• Line two large baking sheets with parchment paper or silicone baking mats with macaron templates. You can make a homemade macaron template by tracing 1.5" circles onto parchment paper. Cover the homemade template with a sheet of parchment paper so it stays clean.
• Separate the eggs while they're cold and then set them aside to come to room temperature for at least 30 minutes. Make sure you don't get any yolk in the bowl with the whites or you won't be able to whip them to stiff peaks. Sift the granulated sugar into a small bowl and set aside.
• Sift the almond flour back and forth between two bowls. Discard any larger chunks left at the bottom of the sifter each time. From the sifted almond flour, measure 100 grams into a large bowl and sift in 135 grams of powdered sugar, 1 and ½ teaspoons espresso powder, and ⅛ teaspoon of salt. Add the dry ingredients to a food processor and pulse for about 30 seconds. Then sift everything back into a large bowl and set aside.

Make the Meringue:

• Add the egg whites to a completely clean and dry bowl or bowl of a stand mixer fitted with a whisk attachment. Begin whipping the egg whites on medium speed for about 30 seconds or until foamy. Add the cream of tartar and whip for another 30 seconds-1 minute until starting to thicken and increase in volume.
• With the mixer running, begin adding the sifted granulated sugar, about 2 teaspoons at a time, and mix for 20 seconds after each addition. Once all of the sugar is added keep mixing until the meringue reaches medium-stiff peaks. If you lift the mixer up out of the bowl and flip it upside down there should be a peak that sticks up with just a slight droop at the tip.

Macaronage:

• In 3-4 additions, use a rubber spatula to gently fold the meringue into the dry ingredients. It will be thick and pasty at first. Keep folding by wiping the sides and bottom of the bowl with a rubber spatula.
• After all of the meringue is added, fold until the batter flows in thick ribbons from your spatula without breaking. If you lift the batter up and draw a figure 8, it should disappear into the batter after about 10 seconds. If it doesn't disappear or if the batter breaks off of the spatula, keep folding and check again after every few turns.
• Pipe the shells: Add the macaron batter to a large piping bag with a ¼-½" round piping tip. Hold the piping bag straight up and down with the tip right in the center of the circle on your template. Squeeze the batter out from the center until it fills the circle, then lift up with a quick twisting motion. See here: How to Pipe Macaron Batter
• Once you have all of the shells piped, lift the pan up and drop or bang it firmly on your counter several times to get rid of any trapped air bubbles.
• Let the macaron shells dry out at room temperature for at least 30 minutes, or until they form a skin on the surface. You should be able to gently touch the tops without wet batter sticking to your finger. 
• Bake: Arrange your oven rack to the middle position and preheat your oven to 300°F/150°C. Bake one sheet of macarons at a time, for 15-17 minutes each. Take the sheet out of the oven and let the shells cool completely before touching or trying to remove them from the pan.

Make the Coffee Buttercream:

• Use an electric mixer to beat the softened butter until fluffy and smooth. Add the powdered sugar, salt, espresso powder, cocoa powder, and cream (or milk), and mix until smooth.
• Once the macaron shells have cooled, use a piping bag to pipe a dollop of frosting onto the bottom of one shell, then gently top with a second shell.
• Once filled, macarons taste best after 24 hours and stay fresh in the fridge for 1 week. They can also be frozen for 1 month.