Line a few trays with parchment paper. You will need at least two, depending on the size of your trays. Normally I use silicon baking mats however, after a few tests I found that they tend to trap too much moisture. The goal is to have a perfectly dried out macaron.
Start by placing the almond flour, powdered sugar, and a half teaspoon of salt into a food processor. Although your almond flour might say that it is "finely ground" it still needs further processing. This helps avoid lumpy macarons. Pulse a couple dozen times and you should be able to tell that the mixture is more powdered than it was.
Using a sifter, tip the contents of the food processor out and gradually sift the dry ingredient mixture into a bowl. This step is very important and also helps with getting a smooth top on the macaron. Once you are done, set the dry ingredients aside.
Carefully crack three eggs into a bowl without puncturing the yolk. Using clean hands, scoop out the yolk one by one and hold it above the bowl so that all of the egg white slides off. Repeat this with the two remaining yolk. I tried using a carton of egg whites for this step, however it can be difficult to figure out the exact volume of three egg whites. Although some information lists it as 30mL per egg white, I found it to be just over 40ml per egg white with the eggs I was using.
Add a half teaspoon of salt to the egg whites and begin to whip. Cream of tartar is also traditionally used as a stabilizer.
Whip the eggwhites until they get fluffy and add the granulated sugar and vanilla extract. Continue to whip them until you get stiff peaks. Sometimes you will get peaks that appear stiff, but if they tip over at all, they are not stiff enough. Properly whipped, the egg whites, now a meringue, will not come out of a bowl even if you tip it upside down.
Grab a spatula and begin adding the dry mixture to the meringue a quarter at a time. When adding it, make sure to fold the merginue and dry mix together by scooping from the bottom of the bowl upwards and folding it over. Continue this until all is incorporated and keep folding. You will know it is ready by doing the figure 8 test. This means you can dip the spatula and pick it up and to a complete, continuous figure as the batter drips off.
Use a little dot of the batter on the underside of the four corners of parchment paper. This helps keep the paper in place while you are piping.
Fill a piping bag with a half inch tip and begin piping small, walnut sized circles of batter onto the parchment paper. Give each bit of piped batter space in case it spreads slightly. Depending on the size of your baking tray, you may be able to fit 6-8 per tray. Once you finish one tray, set it aside, and start on the next.
Pick up each tray and drop them onto the counter to knock any loose air out from under the macarons.
When all the batter has been piped, let it sit on the counter for at least 30 minutes. This is an important step! It causes a film to form over top of the macaron, and will help it retain it's shape while it is baking. If you don't do this, the result might not look as close to what you envision when you picture a macaron.
While waiting, preheat the over to 300 degrees.
Place the first tray in and bake for 15-18 minutes. Do not be tempted to open the over door while it is baking, because this can result in an uneven bake.
Take the macarons out. If they are not perfectly dried out, then you can pop them back into the over for a few more minutes. You will be able to tell when they are ready because they will come off the parchment without sticking at all.
Let them cool completely before adding any filling. You can use any number of fillings, including piping a layer of butter cream.