Combine the ground almonds and confectioners sugar and strain through a sieve twice to remove any lumps. Set aside.
In a clean dry bowl, whisk egg whites until foamy. Once frothy, add a third of the granulated sugar and whisk for a minute. Then, add another third of granulated sugar and whisk for another minute. Finally, add the remaining granulated sugar and whisk for 1 more minute until medium-stiff peaks form. If you are having trouble with peaks forming after several minutes, add a pinch cream of tartar to stabilize the egg whites.
Using a rubber spatula, gently fold in the mixture of ground almonds and confectioners sugar into the egg whites until evenly incorporated. If you want multiple colors, divide your batter and add several drops of gel food coloring. Be careful to not overfold!
Transfer mixture to a piping bag fitted with a plain tip. On a baking sheet lined with a silpat mat or parchment paper, pipe small macaron rounds 1.25" – 1.5" in diameter. Bang the baking sheet firmly against a surface to release trapped air bubbles. Do not skip this step!
Preheat oven to 300ºF/ 150ºC. Allow macaron shells to rest and form a "skin" for about 30 minutes. This may take longer depending on how humid it is, so be patient. To tell when it's ready, you should be able to lightly touch the shell with your finger and not have any batter stick to your finger.
Bake for approximately 15 minutes until they form distinctive macaron feet. Based on your oven settings, this may take less time, so check on your macarons frequently. Remove from oven and let cool completely. This is important!