Line two large baking sheets with parchment paper or Silpat mats. Set aside.
Pour 110g of aged egg whites into the bowl of a stand mixer with a whisk and mix on a medium speed until the surface of the egg whites is covered in small bubbles. Add 1/4 tsp cream of tartar and continue to mix until it reaches the soft peak stage and leaves visible tracks.
Gradually mix 110g of granulated sugar into the egg whites over a few minutes while mixing on a medium-low speed. Increase the mixing speed to a medium-high speed (6 on a KitchenAid). Keep mixing until stiff, glossy peaks form.
Sift 140g of superfine almond flour and 125g of powdered sugar into the meringue. Use a rubber spatula to break up any big clumps and press them through the sieve.
Add in a squirt of yellow gel food coloring if desired. Then fold the ingredients together with a rubber spatula. Use a circular motion that sweeps around the edge of the bowl and then pulls through the bottom of the bowl to make sure everything is getting mixed together. Don't forget to scrape off the inside of the spatula intermittently. Sometimes meringue can get stuck there and not get mixed in properly.
Fold the batter until a thick ribbon of batter runs off the spatula when it's lifted. You should be able to draw a couple of figure 8s with the batter running off your spatula in a continuous stream when it's the right consistency. If the stream of batter breaks before you're able to do this, you may need to stir it a bit more.
Pour the batter into a large piping bag fit with a medium-sized round piping tip and pipe 1 1/2-inch rounds on the prepared baking sheets. Space them about 1 inch apart.
Bang the pans firmly on the counter a few times to release air bubbles, then pop any remaining air bubbles that come to the surface with a toothpick.
Let the macarons rest for 30 minutes, or until they develop a skin. The macarons should look matte once the skin has formed. While the macarons rest, preheat the oven to 320°F/160°C.
Bake one tray of macarons at a time on the middle rack of your oven for 18-21 minutes and rotate the pan halfway through to help the macarons bake evenly. Bake time can vary based on the size of your shells, so if you pipe them smaller than 1 1/2 inches, they may be done a few minutes earlier.
Remove the macaron shells from the oven and let them cool fully on the pan (about 30 minutes), then gently peel them off the Silpat mat. If they're properly baked, they should peel off the mat cleanly and have a shiny bottom.