Macaron recipe from David Leibovtiz; Buttercream adapted from Tartlette
To make the cookies: Line two baking sheets with parchment paper and have a pastry bag with a plain tip (about 1/2-inch, 2 cm) ready. Grind together the powdered sugar with the almond powder and cocoa so there are no lumps; use a food processor.
In the bowl of a standing electric mixer, beat the egg whites until they begin to rise and hold their shape. While whipping, beat in the granulated sugar until very stiff and firm, about 2 minutes. Carefully fold the dry ingredients, in two batches, into the beaten egg whites with a flexible rubber spatula. When the mixture is just smooth and there are no streaks of egg white, stop folding and scrape the batter into the pastry bag (standing the bag in a tall glass helps if you’re alone).
Pipe the batter on the parchment-lined baking sheets in 1-inch (3 cm) circles (about 1 tablespoon each of batter), evenly spaced one-inch (3 cm) apart. Rap the baking sheet a few times firmly on the counter top to flatten the macarons, then bake them for 15-18 minutes. Let cool completely then remove from baking sheet.
To make the filling:
Combine the sugar and egg whites in a double-broiler and whisk until hot but not boiling, about two minutes. The sugar should be dissolved: Pour it into the bowl of a stand mixer fitted with the whisk attachment and beat the meringue on medium speed until it becomes shiny, about four minutes. Add butter, a bit at a time, and beat until smooth. Once butter has been added, beat on high until thick and smooth, about 6-10 minutes. Add in almond extract at the very end. Can refrigerate up to a week or freeze up to a month.