Line two baking sheets with parchment cut to size so that they lie flat and set aside.
In a medium bowl, stir together almond flour and powdered sugar. Using a fine mesh sieve, sift onto a sheet of parchment paper or into another bowl. Scrape the bottom of the sieve with a spatula and discard any remaining large bits of almond flour. Set aside.
In a large mixing bowl, use an electric mixer to beat egg whites on low-medium speed until it becomes frothy like cappuccino foam. Slowly sprinkle in 1-2 tablespoons of granulated sugar at a time and beat on medium speed between each addition. When all the sugar has been combined, keep beating at medium-high speed until the meringue reaches soft peaks. Add the gel food colouring at this point. Continue beating until the meringue reaches stiff peaks.
Add half of the sifted almond flour mixture into the meringue and fold with a spatula until roughly incorporated. Fold in the rest of the almond flour until roughly combined.
Smear the batter against the sides of the bowl to deflate air out of the batter. Scoop it all back up with your spatula and fold a few times. Repeat this motion about 3-4 times and regularly check if the batter is at the correct consistency by scooping up some batter with your spatula and letting it fall back down into the bowl. If the batter smoothly ribbons off the spatula without breaking, it's ready.
Transfer the batter to a piping back fitted with a small round piping tip. Hold the bag perpendicular to the baking sheet, slightly above the surface, and squeeze the batter out, staying in the same spot, and let the batter move outwards into a circle by itself. Do a small, circular flick with the piping tip to stop piping.
Lift and drop the baking sheets onto the counter a few times to bring air bubbles to the surface. Use a toothpick to pop any visible air bubbles. Let the macarons rest on the counter for about 1 hour they are slightly dry to the touch.
Meanwhile, preheat the oven to 290°F. Bake macarons one tray at a time for about 15 minutes or until the tops are just barely wobbly when pushed and bottoms peel off the parchment cleanly. Let cool completely on the baking sheet.