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.
Cherry Jam
Place pitted cherries in a food processor and puree. Add to a small saucepan with the sugar and lemon juice and bring to boil. Simmer for 10 minutes at medium heat, or until thicken. Set aside to cool.
Cherry Buttercream
In a stand mixer fitted with a whisk attachment, add butter and sugar. Mix on low speed until blended and then increase speed to medium and beat for about 3 minutes.
Add vanilla extract and cherry jam and continue to beat on medium speed for 1 more minute, adding some more powdered sugar if too thin to spread.
To Assemble
Pipe a small amount of buttercream on a bottom shell. Top with another shell.
Notes
Age your egg whites. You want to leave the egg whites out at room temperature for a couple hours or in the fridge overnight, which helps dehydrate them.
Use a scale. If there was ever a recipe where a kitchen scale is need, this one is it. You need precise measurements.
DO NOT skip sifting the ingredients. If your almond flour is leaving big chunks after sifting, throw in the food processor and sift again.
DO NOT under whip the meringue. It should have stiff peaks and start to fill the whisk when ready.
Be gentle when folding the dry ingredients in with the meringue. You want to slowly remove some of the air. The consistency is right when it is flowing like lava and you can form a figure eight.
There will be bubbles under the surface once done piping. Use a toothpick to find and deflate them.
If the shells are over baked, just brush a little milk on the bottom before assembling the macarons.