Preheat oven to 310 degrees F. Line two baking sheets with parchment paper and have a pastry bag with a plain tip (about ½-inch, 2 cm) ready. (Setting the pastry bag in a glass while you fill the bag was a great tip I learned during this process.) (Also, I like to double stack the baking sheets.)
Combine the powdered sugar with the almond powder. (Pulse in a blender or food processor if you don’t have finely ground almond meal. A mini food processor works best for this if you have one.)
With an electric mixer, beat the egg whites until they begin to rise and hold their shape. While whipping, beat in the granulated sugar until very stiff and firm, about 2 minutes. (To test to see if egg whites are ready, whip until the tip of the peak doesn’t fold over when you pull the beater out of the meringue.)
Carefully fold the dry ingredients, in two batches, into the beaten egg whites with a flexible rubber spatula. When the mixture is just smooth and there are no streaks of egg white, stop folding and scrape the batter into the pastry bag. (You can put a spoonful on a plate to test it. If it slowly flattens out it’s perfect. If it runs, add a bit more almond flour/powdered sugar. If it just stays in a blob, give it a few more folds.)
Pipe the batter on the parchment-lined baking sheets in 1-inch (3 cm) circles (about 1 tablespoon each of batter), evenly spaced one-inch (3 cm) apart.
Rap the baking sheet a few times firmly on the counter top to flatten the macarons. Leave out, uncovered for 15 minutes, then bake them for 15-20 minutes. Give the macs a gentle little shake with the tip of your finger to see if they're done. You want them set but not firm. It’s better to undercook them.
Let cool completely then remove from baking sheet.