Heat oven to 300°F. It's helpful to have an oven thermometer to monitor the temperature.
Wipe down all bowls and whisk attachment with a little white vinegar on a paper towel to remove any leftover oils.
Separate egg whites from yolks and allow egg whites to come to room temperature.
Measure dry ingredients using a kitchen scale. Sift almond flour and confectioners sugar together into a large metal or glass bowl.
Print off the macaron template. Place them on a sheet pan underneath a piece of parchment paper.
Prepare your piping bag with a round tip. Push part of the side of the piping bag into the piping tip to ensure nothing leaks out. Set the bag inside a tall glass, and pull the remaining top of the piping bag out over the outside of the glass to make pouring the batter easy and clean.
For the Macarons
Add in room temperature egg whites to a large bowl, along with cream of tartar. Whip on medium-low speed with a handheld mixer until eggs are very foamy. Then add ⅓ of the granulated sugar at a time, and increase the speed to medium high.
Once all the granulated sugar is incorporated, allow egg whites to continue to whip up on medium-high speed until stiff peaks form (you'll notice the meringue starts to ball up inside the whisk). To test the meringue stiffness, pull the whisk out. A stiff peak should stand straight up (no curl at the tip). You'll also know it's ready because you can fully flip the bowl over and nothing moves or falls out. Make sure not to over beat the meringue at this stage.
Pour a third of the sifted almond flour & confectioners sugar into the meringue mixture. Gently fold in the egg whites using a silicone spatula. Continue until all the meringue is fully incorporated and no dry bits of almond flour remains on the bottom of the bowl.
Evenly divide the batter into 3 medium-sized metal or glass bowls. Add 1-2 drops of gel food coloring. Then, begin working the batter until everything is fully incorporated (this is called the macaronage process). Slowly, spread the mixture along the side of the bowl, then wipe it back down. Be sure to do this gently. Repeat, until the mixture has reached a smooth, shiny, flowing consistency. You can test this by lifting your spatula and seeing if the batter drops almost like lava. Once the batter drops back into the bowl, it should take about 10-15 seconds for the ribbon that formed to "disappear" back into the rest of the batter.
Spoon each color of batter in a straight line on a piece of plastic wrap. Careful roll the plastic wrap up so all the colors are enclosed. Cut off the tip of one end of the plastic wrap, and insert it open side down into a prepared piping bag. Hold the bag vertically, and gently pipe the batter out until it reaches the inside line of the circle template. Continue until no batter reamins.
Gently tap the sheet pan down the counter a few times to release any air bubbles. Pop any air bubbles with a toothpick. Allow the batter to sit on the counter and dry for 20 - 40 minutes, just until a thin "skin" develops, and you can touch the tops without ruining the macaron. This resting time will vary depending on the humidity (make sure you don't let them rest too long by periodically checking on them). While the macarons are drying, heat oven to 300°F.
Bake for 15-18 minutes on the middle rack of the oven, rotating the pan halfway through the cooking process. Remove from the oven and allow to cool for 5 minutes on the pan. Then, move silicone mat or parchment pack to a cooling rack until completely cooled.
For the Amercian Buttercream
Add the paddle attachment to your stand mixer. To the stand mixer bowl, add butter. Cream on medium-high speed for 2-3 minutes until light and fluffy.
With the mixer on low, gradually add in confectioners sugar.
Bump up the speed to medium, and add in heavy whipping cream, vanilla, and salt. Continue to mix for an additional 5 minutes until the frosting is light and fluffy.
Match up macaron cookies so they are paired with a similar size/shaped cookie. Pipe buttercream on one side of the macaron shell using a Wilton 1M tip. Gently place matching side on top on the buttercream.
Mature the macarons with the filling in the refrigerator overnight. This will allow the macarons to slightly soften and develop a deeper flavor.
See blog post for your full guide to macaron troubleshooting problems.