TIP: This recipe will come out best if you weight out each ingredient using a kitchen scale.
Sift together confectioners sugar and almond flour, set aside.
Beat room temp egg whites and salt together on medium speed for 1 minute. Switch to high speed and bean until stiff peaks form (I would check mixture every 30 seconds so you do not overbeat the egg whites, took my egg whites about 1 minute on high)
Gently fold in your sifted granulated sugar 1 tablespoon at a time.
On low speed, bean in any flavoring or coloring of your choice. Only mix in flavoring/coloring until just combined. (Be sure not to overmix)
Do not use a hand mixer or stand mixer for this step! Using a rubber spatula, gently fold in the confectioners' sugar/almond flour mixture until combined. Be very gently as you fold in the dry ingredients. Once combined your mixture will be smooth, sticky and glossy.
Let batter sit uncovered at room temp for 10-30 minutes.
As batter sits out prep your piping bag using a 1/2 inch circle tip for piping batter onto baking sheets. Traditionally silicone baking sheets are preferred but I use parchment paper and that has worked great for me!
Fill the piping bag with batter and pipe even round circles onto the parchment covered baking sheets. Keep piping bag close to baking sheet holding it upright to get an even circle as you pipe. Make each circle about 2-inches, batter will slightly spread as you pipe. Gently tap bottom of baking sheets after your finished piping to remove any large air bubbles.
Let your piped macaroon shells sit out to form a dry shell for 45 minutes - 1 hour. This step is SUPER IMPORTANT so don't skip it!
Preheat oven to 325 (Do not preheat until macaroons have finished sitting out so you do not create a lot of humidity in your kitchen) Bake macaroons for 9-10 minutes, one baking sheet at a time. If you have a convection oven do not use the fan. Just stick to it as a normal oven. Allow macaroons to cool completely on the baking sheet before removing and filling.
Fill piping bag with buttercream frosting (or desired filling) and pipe a ring around the edge of a macaroon shell. (Use a 1/2 inch circle piping tip). Gently press together macaroon shell with buttercream to another empty macaroon shell and VIOLA! You did it! You Made French Macaroons!