Add the room temperature egg whites to a large, clean bowl, or the bowl of your stand mixer fitted with the whisk attachment. Whip the egg whites until foamy, about 30 seconds, then add the cream of tartar and whip for another 30 seconds until starting to thicken.
In 3-4 additions, add the granulated sugar and mix for 20 seconds after each addition. Once all of the sugar is added, whip the meringue until it reaches soft peaks (peaks that flop to the side). Add the gel food coloring (if using) and continue to whip to stiff peaks (peaks that stick straight up).
Macaronage: In 3 additions, add the sifted dry ingredients to the meringue and use a rubber spatula to gently fold in each until the batter is smooth with no pockets of flour remaining.
After the last addition, continue to fold by wiping the sides and the bottom of the bowl until the batter is at the right consistency. When you lift the spatula up, the batter should flow continuously in thick ribbons without breaking. Lift the batter up to check often and stop folding as soon as it gets to the right consistency.
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. Gently squeeze the bag until the batter spreads and almost fills the circle. Stop squeezing and lift up with a quick twisting motion.
Once you have all the shells piped, lift the pan up about 5" and drop or bang it firmly on your counter several times, you should see little air bubbles come up to the surface and pop. If you see any large bubbles that don't pop, use a toothpick to pop them yourself.
Let the shells dry out on the pan 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.
Arrange your oven rack to the middle position and preheat your oven to 300°F/150°C.
Bake the macarons, one baking sheet at a time, for 12 minutes each. Take them out of the oven and let cool completely before touching them or trying to remove them from the pan.