Prep. Line three baking sheets with parchment paper (or baking mats) and set aside.
Make the meringue. Place the egg whites in your mixer's bowl and mix until frothy. Gradually add 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. Use any color you like. Set aside.
Sift the dry ingredients. Sift together the almond flour and powdered sugar into a large mixing bowl. With a large spoon or whisk, 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. Set aside and let them dry at room temperature for 1 hour.
Bake. Preheat the oven to 315ºF. Slide the baking sheet into the preheated oven and bake the macarons for 12 to 15 minutes; the cookies are done when they no longer jiggle when you touch the tops. Rotate the baking sheet after 6 minutes for even baking.
Cool. Remove the macarons from the oven. Do not remove them from the baking sheets; place the sheets on a cooling rack and let the macarons cool completely.
Make the Filling
Make another batch of meringue. In a small mixing bowl, beat the egg whites and salt. Gradually add in the sugar, and continue beating until soft peaks form.
Add the corn syrup. Microwave the corn syrup on high for 1½ to 2 minutes, or until boiling. Then, slowly stream the corn syrup into the egg whites, beating until the mixture is stiff and glossy. Add the 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 before serving.
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.
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.