1. Whip the meringue. Whip the egg whites and granulated sugar on medium-high speed to stiff peaks. Meringue is done when it looks like shaving cream, and the peaks coming off the mixer paddle curve slightly, almost sticking straight up. 
2. Macaronage: Sift the almond flour, salt, and powdered sugar directly into the bowl with the meringue. Discard any large pieces remaining in the sifter or sieve. I like to mix the ingredients a bit rough at first to bring them together. Then fold gently, scraping around the sides of the bowl and up over the top of the batter. You want a macaron batter that is smooth, shiny, and ribbons off the spatula. Any batter drizzled off the spatula should settle back into the collective mass in ten or twenty seconds (a long moment). 
3. Pipe the batter. Immediately transfer your batter to the pastry bag. To pipe macaron batter, hold the bag vertically and about a quarter of an inch above the pan. Squeeze until you just about reach your desired size or the inside edge of the guides. Immediately stop squeezing and flick away the pastry tip in a circular motion. 
4. Rest the batter. Drying out the tops of the shells a little can help them rise evenly when they hit the oven. And maintain a smoother dome shape. Let the pans sit on the counter for 10 to 20 minutes before baking. 
5. Bake: Bake the macarons at 290-300 F until the tops are dull and the batter is set, between 14 to 18 minutes. An easy way to check is to gently nudge the top of a couple of macarons with your finger. If the tops don't shift away from the bottoms, they are done. You can also lift a corner of the parchment or baking mat and check the bottoms. If the shell sticks, bake a few minutes longer. Remove the baked macarons from the oven, and cool for a few minutes on the pan. As soon as you can handle the shells, gently peel them off by pressing up from underneath the parchment or baking mat.

Fill & Serve

1. Match your baked shells into like-sized pairs. Any odd macarons are for the baker. 
2. To pipe your filling, transfer it to a piping bag or plastic baggie and snip a tiny hole at the corner. Leave space between the edge of the shell and the filling. This is the classical, professional standard. Macaron fillings should not be right up to the edge of the shells. The mound of filling should not be as high as the shells. Otherwise, the fillings will ooze out when you take a bite. 
3. Store finished macarons in the refrigerator. But always serve at room temperature. Unfilled shells can be packed carefully and frozen.