Prep. Line three baking sheets with parchment paper; set aside.
Make the meringue. Place the egg whites in your mixer's bowl and mix until frothy. Gradually pour in the superfine sugar, and continue beating until the mixture is glossy and forms stiff peaks.
Add color (optional). At this point, you may want to add in a few drops of food color and mix just until combined. Set aside.
Sift the dry ingredients. Sift together the almond flour and powdered sugar into a large mixing bowl. With a large spoon, mix well to incorporate the almond flour and sugar.
Mix the batter. Using a rubber spatula, gently fold in ¼ of the meringue into the almond mixture. Continue folding in the remaining meringue until completely incorporated.
Pipe the macaron shells. Fit a piping bag with a ⅜-inch round tip and fill it with the macaron mixture. Pipe the batter into small rounds onto the prepared baking sheets. Allow to dry at room temperature for 1 hour.
Bake. Preheat oven to 315ºF. Bake the macarons for 12 to 15 minutes; cookies are done when they no longer jiggle when you touch them on top. Rotate the baking sheet after 6 minutes for even baking.
Cool. Remove the macarons from the oven. Do not remove them from baking sheets, but place them on a cooling rack. Let them completely cool.
Make the Filling
Make another batch of meringue. In a small mixing bowl, beat egg whites and salt. Gradually add sugar, and continue beating until soft peaks form.
Add the corn syrup. Microwave corn syrup on high for 1 ½ to 2 minutes, or until boiling. Slowly stream the corn syrup into the egg whites, beating until the mixture is stiff and glossy. Add vanilla and beat until thoroughly combined.
Pipe the filling. After the macarons have completely cooled, turn half of the caps on their backs. Pipe about ½ teaspoon of the filling onto each bottom shell. Close the macarons with another cap.
Rest. Once all of your macarons are assembled, put them in an airtight container in the refrigerator and let them rest for 24 hours.
Notes
Do not overmix. Overmixing will make the cookies crack. Mix just until combined and then leave it alone.
Allow the shells to dry. Once you pipe out the cookies, let them dry for one hour before baking. Get to know your oven.
Don't overbake. Check the macarons at the earliest suggested baking time, and don't overbake.
Let them fully cool. Assemble the macarons when they are completely cooled.
Rest before serving. Macarons taste best after 24 hours. Once all of your macarons are assembled, put them in an airtight container, place them in a cool place (or in the fridge), and let them rest for 24 hours