Line two large baking sheet pans with silpat mats or parchment paper. Fit a piping bag with a small round tip (Recommendation: Wilton #10).
Set a heatproof bowl over a small saucepan of simmering water, making sure the bowl isn’t touching the water.
Add the egg whites and granulated sugar to the bowl. Whisk constantly until the sugar has fully dissolved (approx. 3-4 minutes). Transfer the egg white mixture to the bowl of a stand mixer fitted with the whisk attachment.
Beat the egg whites on medium-high speed (Kitchenaid #8) until stiff peaks form.
Sift the powdered sugar and almond flour into the beaten egg whites. Fold the mixture gently to incorporate the dry ingredients into the egg whites. (See Note 3 for proper folding technique). When half of the dry ingredients have been incorporated, add the food coloring, if using, and continue folding.
Gently deflate the meringue by smashing it against the sides of the bowl and folding it back together. Repeat the smashing process 3-4 times and then test the meringue to see if it’s at the “figure 8 stage”. If you can draw an 8 with the batter while it flows smoothly, it’s ready. If the meringue falls off in clumps or breaks during the “8”, smush it 1-2 more times and fold it back together. Then repeat the figure 8 test.
When the batter flows smoothly, transfer the mixture to the piping bag fitted with a round tip.
Pipe 1.5” circles about 2” apart on the silpat lined baking sheet. Make sure to hold the piping bag perpendicular to the baking sheet so you don’t end up with uneven macarons.
Immediately after you’ve finished piping the tray, hold it 6” off the counter and drop it straight down to release any air bubbles. Repeat the dropping process 5-6 times, or until it looks like any large air bubbles have popped.
Set the baking sheet aside to rest for 20-25 minutes, or until the macarons have developed a skin. The macarons are ready to bake when they can be gently touched without sticking to your finger.
While the macarons rest, preheat your oven to 325F (see notes). Bake the macarons one tray at a time for 14-16 minutes, rotating the tray halfway through baking. The macarons are finished when they peel easily off the silpat.
Allow the macarons to cool on the tray. Once they are fully cooled, they can be filled and aged.