First, combine all dry cookie ingredients in a bowl and sift several times with a fine mesh strainer until very fine. In another bowl, beat egg whites with a pinch of salt for 1 min, then slowly add granulated sugar, continuing to beat, until stiff peaks.

Fold the dry ingredients into the egg whites slowly until all the dry ingredients are absorbed and the dough resembles coarse sand. Place dough into a piping bag.

On a parchment-lined baking sheet, pipe dough into ~1.5 inch circles. Once piped, tap pan against table several times to flatten out the dough balls.

Let dough rest for 1hr and then preheat oven to 300 degrees and bake for 17-19 minutes (make sure not to open the oven prematurely, as this could deflate them!). Let cool to room temp while you make the batter.

For the batter, beat butter in a bowl, add sifted powdered sugar and cocoa powder, and continue beating until combined.

Pipe a dollop of filling onto a cookie and add another cookie to make a macaron. Repeat with remaining cookies and try to wait at least 12h stored at room temp (for filling to dry) before eating.