Preheat oven to 300˚F /150˚C, and position the oven rack in the center of the oven. Using a round cookie cutter or the base of a glass (something about 1.5 inches in diameter), draw a "template" for your macarons your parchment papers, leaving about 3/4" between each circle. Here is one you can print and trace. Flip the parchment paper over so that the side you drew on is touching the baking sheet.
Combine the almond flour and powdered sugar together in a large bowl. Sift or pulse the mixture in a food processor, to ensure there are no large lumps and that the mixture is properly aerated. Set aside.
Remove the bowl from the mixer. Add half of the almond flour and powdered sugar mixture, and fold into the meringue. You want to deflate the meringue just a little at this stage, to combine the meringue and ground almond mixture.
Add the remaining almond flour mixture, and stir lightly to combine. Now you are going to "macaronage" the batter until you get the right consistency. Fold the mixture in a series of 'turns', deflating the batter by spreading it against the side of the bowl. Turn the bowl slightly and repeat the movement - scooping the batter from the bottom of the bowl, and spreading it against the side. Continuously check the consistency of the batter - you want it to flow like lava when you lift the spatula from the bowl, and you should be able to 'draw' a figure 8 with it, without the batter breaking (see video #2 above). This step can take some practice until you know what it should feel and look like. If in doubt it is better to under-mix them than over-mix them - the process of putting the batter into the bag and piping out will help mix a little too.
Macarons taste best if you 'mature' them in the refrigerator overnight to let the flavors come together, if you have patience for that. Bring to room temperature before eating. They're delicious eaten the same day as well, which is recommended if using a fresh berry on the inside.
Store leftovers in an airtight container in the fridge or freezer. If freezing, defrost in the refrigerator for 3 hours and then bring to room temperature before enjoying them.
Source: Macaron Shell adapted from Cloudy Kitchen; Buttercream from America's Test Kitchen
The buttercream recipe will be enough for a scant amount of filling. Double it if you want to ensure plenty of filling.
The yield will depend on the size of your macarons, but I generally get about 48 filled and assembled.