Line two half sheet baking sheets with silicone baking mats or parchment paper. (If you wish to use parchment, make sure the parchment lays perfectly flat so you don’t end up with lopsided macarons. You can tape the parchment temporarily to help keep it secure while piping and then remove the tape before baking.)
Fill a small saucepan halfway with water and set it over medium heat. Then, place a heatproof bowl over the pan, making sure it doesn’t touch the water.
Add the egg whites and granulated sugar to the bowl and whisk constantly until the sugar has completely dissolved. This will take about 2 to 3 minutes. (Test to make sure the sugar is dissolved by rubbing the mixture between your fingers. If it’s smooth, it’s ready to go. If the mixture feels grainy or sandy, keep whisking for another minute or so and then try again.)
Transfer the egg white mixture to a clean, dry bowl of a stand mixer fitted with the whisk attachment. Beat on medium high until the mixture forms stiff peaks, about 5 minutes.
Sift the powdered sugar and almond flour into the egg whites.
Gently fold the mixture together, making sure to scrape down the sides of the bowl as you fold. Take your time and be careful that you are not deflating the egg whites just yet.
Gently fold the dry ingredients into the egg whites, making sure not to deflate the egg whites. Make sure to scrape the sides of the bowl as you fold.
Once all of the dry ingredients have been incorporated into the egg whites, add the gel food coloring, if using. (see notes below) Continue folding the meringue but this time begin gently smushing the batter against the sides of the bowl in a circular motion, then scrape down the sides of the bowl and fold it all back together. Repeat this deflating process until the batter flows smoothly off the spatula. (On average this takes about 5 smush and folds but will be dependent on how much you deflate the egg whites each time.)
You can test the batter’s consistency by slowly drawing a figure 8 with the batter. If the you can make an “8” with the batter flowing off the spatula in a constant stream, it’s ready! If it breaks or falls in clumps, smush and fold a few more times until the desired consistency is achieved.
When the meringue flows smoothly, transfer the mixture to a piping bag fitted with an open round tip. A #12 piping tip or #10 tip works perfectly. Pipe 1” circles or egg shapes about 2” apart holding the piping bag perpendicular to the surface. Using a silicon macaron mat will help with this step. Once you’ve finished piping one tray, tap the tray firmly on the counter or drop straight down onto the counter five or six times to release any air bubbles. Repeat for the second tray. The shells will flatten slightly.
Let the shells rest for about 30 minutes or until the tops feel dry to the touch (this is called developing a skin). This can take up to an hour.
While the shells rest, preheat your oven to 325°F (you can check the oven temperature using an oven thermometer – this is especially helpful if you think your oven runs a little hot)..
Bake the shells one baking sheet at a time for 12 to 15 minutes, rotating the baking sheet halfway through if necessary. The shells are done when they don’t move or jiggle about when the baking sheets are moved. Allow the macarons to cool before removing them from the tray.