Place the confectioners' sugar and almond flour in a food processor or blender and pulse or blend for 30 seconds until thoroughly combined and fine in texture. Set aside.
In a completely dry and grease-free bowl, beat the egg whites and salt together on medium speed for 1 minute. Switch to high speed and beat *just* until stiff peaks form, about 3 minutes. Do NOT overbeat. Using a metal spoon or rubber spatula, gently fold in the sifted granulated sugar, 1 Tablespoon at a time.
On low speed add in your vanilla extract. Do not over mix.
Using a metal spoon or rubber spatula, fold in the confectioners' sugar/almond flour mixture until combined. Be very gentle and light-handed while doing so. Once completely combined, the mixture will be smooth, sticky, and glossy.
Let the batter sit uncovered at room temperature for 10-30 minutes. Meanwhile, fit your piping bag with the piping tip. Line 2-3 baking sheets with silicone baking mats (read explanation in this post about why these mats are preferred).
Fill the piping bag with the batter and pipe evenly sized rounds onto the baking sheets-- make sure you are holding the bag vertically and close to the baking sheet. While piping, the batter will slightly spread out, so keep that in mind. You want around 2-inch circles. Gently tap the bottom of the baking sheets on your counter to rid any large air bubbles.
Let the piped rounds sit for at least 45 minutes and up to 1 hour. This is crucial to making macarons! The air will will help the rounds set and form a dry shell. They should not be sticky going into the oven.
Preheat oven to 325°F (163°C). Bake the macarons for 10 minutes, one baking sheet at a time. Rotate the pan at the 5 minute mark. The tops should be crisp and the macarons should have formed their signature crinkly "feet." Allow to cool completely on the baking sheet before filling.
Fill and sandwich two shells together to form an iconic French macaron cookie! Leftover macarons keep well covered at room temperature or in the refrigerator for up to 1 week.