Sift together the almond flour, powdered sugar, cocoa powder and salt in a medium bowl. Set aside.
In a large bowl, beat the egg whites on medium speed until foamy, about 1 minute. Gradually add the granulated sugar in thirds, waiting about 30 seconds between each addition.
Once the egg whites start turning white, add the cream of tartar and whip on medium until soft peaks fork. Add the vanilla and whip on medium-high until you get stiff peaks.
Add the sifted flour mixture to the egg whites and start folding gently, forming a letter J with the spatula. You want to stop folding when the batter is glossy and flows like lava. If you lift the spatula with some batter, you should be able to make a figure eight pattern without the batter breaking up.
Transfer the batter to a pastry bag with a large round piping tip. Pipe 1 ½" circles on a parchment or silicone-lined baking sheet. Tap the baking sheet against the counter a few times to release the bubbles. Use a toothpick to remove any remaining pockets of air.
Let the shells sit out at room temperature for 30-60 minutes or until the tops are dry and don't stick to your finger when you touch it.
Preheat the oven to 325ºF. Bake for 12-14 minutes, rotating halfway through. The tops should be crisp and the macarons should have formed feet. Allow to cool completely on the baking sheet before filling.