How to Make It
Combine powdered sugar and almond flour in a food processor. Process for 30-40 seconds, or until mixture has a very fine and light texture.
Whip egg whites with an electric mixer on medium-high speed until soft peaks form. With mixer running, slowly add granulated sugar and vanilla. Continue whipping until stiff peaks form.
Gently fold almond flour mixture into egg whites, being careful not to overmix. The final mixture should be smooth and glossy.
Line two baking sheets with parchment paper or silicon baking mats. Transfer macaron batter to a piping bag with a small round tip. Pipe 2-inch circles, about an inch apart, on both baking sheets. Tap baking sheets against the counter to release air bubbles.
Let the macarons shells rest in a dry place for 20-30 minutes, or until you can touch the shells without the batter sticking to your fingers.
While cookies are drying, preheat oven to 350°F. Place 1 baking sheet of cookies on bottom oven rack of preheated oven, and immediately reduce temperature to 300°F. Bake cookies 16 minutes. Crack oven door open, and continue baking with oven door ajar until edges of cookies can be gently lifted from parchment, 5 to 8 minutes. Cool completely on baking sheet, about 20 minutes. Repeat process with remaining cookies, making sure to return oven temperature to 350°F before placing baking sheet in oven and reducing temperature to 300°F.
Gently remove cookies from parchment paper. Pipe desired filling onto half of the cookies (about 1 tablespoon per cookie); top with remaining cookies to form a sandwich.