Line two half sheet pans with silicone mats (I like the ones that have the circle pre-marked on the mat - found on Amazon, see blog post for link). You could also use parchment paper.
In a medium bowl, whisk together the almond flour and powdered sugar (make sure you get out any lumps). Weigh out the ingredients for best results. Set aside.
Place egg whites in a heat proof bowl. I like to weigh the 3 egg whites. If they are less than 100g, then add enough liquid egg whites (from the carton) to reach the 100g mark. Add the granulated sugar. Place bowl over a pan of boiling water, whisking constantly for 90 seconds. This will dissolve the sugar. Remove the bowl from the heat and immediately start beating with an electric mixer with the whisk attachment on medium high for 1 minute, then turn up to high and beat 2 minutes or until stiff peaks form. (Do not overbeat or they will be too dry.)
Fold half of the almond flour mixture into the beaten egg whites until combined, then fold in the remaining half of the almond flour mixture. Keep folding until completely combined. Add the food coloring. Continue to fold and stir until you have a smooth batter that runs off the spatula easily and fairly quickly. You should be able to drizzle a figure eight pattern. This took me 6 minutes. Note: You will need to use some "elbow grease" towards the end, meaning to put some muscle into it. You will be delicate with it at first, when you're folding, then you don't have to be so delicate towards the end.
Pour batter into a large pastry bag fitted with a 1/2" round pastry tip. Start piping the batter, holding the bag at a 90° angle. Squeeze bag until you've piped a round of macaron batter that almost reaches the edges of the macaron template or about 1 3/8-inch wide. You should have enough to pipe about 40 shells. Tap pan on counter to release the air bubbles. Use a toothpick to pop any bubbles that appear. Let the shells dry for 40-60 minutes. You can preheat the oven at this point to 325°F. Bake the shells for 16-18 minutes. Let them cool completely. Use a metal spatula to slide underneath the macaron shell and lift from the pan. Don't use your hands, the shells might break. Note: Ovens may vary. If you want to TEST bake one cookie first, you could do that. If they aren't baked long enough, they will be too soft, but baked too much and they will be too hard.