In a clean and dry medium mixing bowl, sift almond flour. Replace any large grains that do not go through the sifter. Then, sift in the powdered sugar. Finally, sift the almond flour and powdered sugar together. Set aside.
Measure out your granulated sugar into a cup or bowl. Make sure all bowls and utensils are dry, clean, and oil free. It helps to wipe everything down with vinegar or lemon juice.
In a clean and dry mixing bowl, place your room temperature egg whites. Begin beating the egg whites on low speed until frothy bubbles form. Add cream of tartar. Continue beating until the bubbles become smaller and more crowded. While beating, slowly add the sugar in thirds, incorporating well before adding the next batch. Raise speed to medium-low and continue beating until soft peaks form. Raise speed to medium-high at most and continue beating until stiff peaks form. If you're not sure what stiff peaks look like, please read notes above. The process took me 15 – 20 minutes using a hand mixer.
Add 1/3 of the almond flour and powdered sugar mixture into the meringue. Use a spatula to fold and incorporate the dry ingredients. Fold in a "J" motion, bringing the spatula down and then looping back up and over. Add the remaining almond flour and powdered sugar and continue to fold, smearing the spatula against the sides of the bowl to remove air from the batter. After a minute of folding, check the consistency of the batter. It should flow off the spatula in a continuous ribbon, and you should be able to create a "figure 8" shape when you move the spatula. If the batter is too thick, continue folding and checking.
Once the batter is at the right consistency, add the espresso powder. Fold 2 - 3 times to gently incorporate the powder.
Place the batter in a piping bag fitted with a 1/4 inch round piping tip. Pipe 1 inch circles onto parchment paper or a silicon mat on a baking tray. I like to flip my baking trays upside down to create perfectly smooth surfaces.
Tap the tray against the counter ~5 times to release air from the shells. Then, take a toothpick and pop any air bubbles that you see.
Let the macarons rest for 30 minutes to 1 hour until a "skin" forms. The macarons should be matte instead of shiny, and you should be able to gently touch the top without batter sticking to your finger.
While the macarons rest, preheat the oven to 325°F. If you have an oven thermometer, use it to make sure the oven temperature is accurate.
Once skins have formed, bake the macarons one tray at a time for 11 - 14 minutes until the shells are set. They should not jiggle in the center.
Remove from the oven at let cool completely before filling. Cooled macarons should peel easily off the tray.