Heat a small pot of water over medium heat until it steams. In the bowl of a stand mixer, combine egg whites and granulated sugar. Place bowl over steaming pot, creating a double boiler.
Whisk egg whites and sugar until sugar melts completely and egg whites become white and frothy, 1 to 1.5 minutes. Remove from heat and place bowl back onto standing mixer.
Fit standing mixer with whisk attachment and whisk on high speed for 2-3 minutes, until stiff peaks form. Congratulations, you just made a Swiss meringue!
Sift together almond flour, cocoa powder, and powdered sugar, then gently shake into meringue bowl.
Place bowl onto stand mixer fitted with a whisk attachment. Turn mixer to medium speed and whisk for 10 seconds. Stop mixer and use a spatula to scoop up some of the batter. If you can make a figure-eight with the dripping batter without the batter breaking, you can stop. But most likely you will need another 5-10 seconds. So repeat process, and try the figure-eight again. The best way to describe the perfect consistency is like slow moving lava. It should give, but only slightly, like in slow-motion.
Once your batter is the correct consistency, scoop it into a large pastry bag fitted with a 1 inch tip. Pipe silver dollar-sized circles onto prepared baking sheets, keeping about 1.5 inches between each meringue. Bang baking sheet on counter two times to remove any air bubbles.
Here’s the fun part: you don’t need to let them air dry. Just pop them into the prepared oven for 13 minutes, turning around halfway through, then allow to cool completely before removing from baking sheets.
While the macarons are baking, make the marshmallow filling. Make a double boiler with a heat safe bowl. Use a whisk to beat egg whites and sugar for the marshmallow filling until frothy and white and the sugar granules have dissolved. Transfer the mixture to stand mixer (or get a heck of a workout doing it by hand) fitted with the paddle attachment. Beat on high speed until the mixture is smooth and glossy and medium stiff peaks form.
Scoop mixture into a piping bag fitted with a star tip and set aside until ready to assemble the macarons.
Once you’re ready, pipe the filling onto a macaron and sandwich with another macaron. Repeat with all macarons. Optional: garnish with melted chocolate!