In a medium bowl, scale the 138g almond meal, 120g powdered sugar, and 8 grams of cocoa powder. Sift all of them into a larger bowl and discard any large pieces. Set aside.
120 grams powdered sugar, 138 grams almond meal, 8 grams cocoa powder
In a stand mixing bowl, add the 107g room temperature egg whites and begin whisking on medium speed (speed 3-4) for 1-2 minutes. When the whites get foamy, add the cream of tartar.
107 grams egg whites, room temperature, ¼ teaspoon cream of tartar
Very slowly, begin adding the 110g sugar by the spoonful, sprinkling it into the whites as they whip. When all of the sugar is added increase the speed to medium high (speed 5-6). Whip for about 6-7 minutes or until stiff peaks form.
110 grams sugar
Add the whipped egg whites to a large bowl.
Add ⅓ of the almond meal/sugar mixture to the whites. Fold very gently with a spatula until combined. The add the next ⅓ and fold to combine. Continue until all of the dry ingredients are incorporated.
Using your rubber spatula, scrape the batter against the side of the bowl. Every few scrapes, pick up the batter and let it fall into the bowl. The batter should flow slowly in ribbons. Try to make a figure 8 with the batter. If it falls without breaking, its ready!
Line an upside down pan with parchment paper or silicone baking mat and fill a piping bag and round tip with the batter. Pipe directly over the top of the parchment. When the pan is full, rap and drop the pan on the counter to release any air bubbles. You can use a tooth pick to pop any bubbles that come to the surface.
Preheat your oven to 300. (If your oven in on the hotter side, lower temperature might be better ie: 275-285)
Allow the macarons to sit out to dry and form a skin. This can take anywhere from 30 minutes to an hour depending on the level of humidity in your house. They are ready to bake when the shell can be touched without it sticking to your finger or leaving an impression.
Bake each tray for about 13-14 minutes. The macarons are done baking when you gently touch the top of the shell, it should just barely budge from the foot. Allow to cool completely before filling!