Pulse powdered sugar and almond flour in a food processor until fully combined
Sift sugar and flour mixture one more time; set aside (DO NOT SKIP this step, or you will have lumpy macarons)
Whip egg whites on medium low speed until frothy. Add cream of tartar.*
Resume whipping and begin "raining" in sugar slowly into the egg whites. Keep mixer at medium.
One you reach firm peaks, and the meringue is balled up in your mixer whisk, remove from mixer. Fold in 1/3 of the sugar/flour mixture.
In two more installments, fold the remaining mixture into the egg whites until fully incorporated.
Macaronage - using the back of your spatula, paint or push the batter of the sides of the bowl in a flower-like pattern. Scrape back down to the bottom of the bowl and paint up the sides again, effectively deflating some of the air.
Test the consistency by drawing a figure eight batter with the batter dripping off the spatula. If you can draw an eight without it breaking, and the batter sinks back into itself within 10-15 seconds, macaronage is complete. If not, repeat "painting" one more time, then test again.
Fit piping back with medium round tip and add batter. While holding piping bag at a 90 degree angle, squeeze batter onto template, twisting your wrist at the same time you release pressure at the end.
Rap tray on counter several times, rotating the pan to knock out air bubbles. If any are remaining, they can be popped with a toothpick.
Preheat oven to 310 and place an empty cookie sheet in very top rack of oven. (use one you don't need, as it will stay there through the entire baking process)
Rest, uncovered until a skin is formed. You should be able to gently touch the batter and not have any stick to your skin.
Bake in center of oven for approximately 20 minutes. This number is not firm - it will be different for each size cookie, each oven, and other details that affect baking macarons (such as weather).
To test if they are done, try to pick one up off the tray. If it lifts up and has a smooth bottom, they are done! If not, leave them in another minute or two.
Remove and let cool on tray, then transfer to cooling rack.