Line 3 rimmed baking sheets with silicone macaron baking mats.
Within the work bowl of a meals processor, pulse flour, confectioners’ sugar, and cocoa till finely floor and absolutely mixed. Sift combination by a big fine-mesh sieve into a big bowl, discarding any solids. Add 2 egg whites (60 grams); fold till mixed. Cowl with plastic wrap to stop drying out.
In a small saucepan, stir collectively granulated sugar and 1⁄4 cup (60 grams) water. Cook dinner over excessive warmth, with out stirring, till an instant-read thermometer registers 240°F (116°C) to 245°F (118°C).
In the meantime, within the bowl of a stand mixer fitted with the whisk attachment, beat cream of tartar and remaining 2 egg whites (60 grams) at low velocity till foamy. Improve mixer velocity to medium-high, and beat till medium-stiff peaks type. (Egg whites and sugar syrup needs to be ready so they’re prepared on the identical time.)
With mixer on excessive velocity, add sugar syrup to whipped egg white combination, fastidiously pouring straight into combination, avoiding facet of bowl and whisk. Beat till combination is cooled and stiff peaks type, about 4 minutes.
Add one-fourth of meringue (about 1⁄2 cup or 60 grams) to flour combination; stir vigorously till mixed. Add remaining meringue, and punctiliously fold till combination is ribbon-consistency. (Combination needs to be thick and slowly however freely fall off the spatula in a “V” form; once you drag the spatula by the batter, it ought to transfer like lava and slowly come again collectively.)
Switch batter to a pastry bag fitted with a medium spherical piping tip (Ateco #804). Holding piping bag with opening of tip perpendicular to a ready pan, pipe batter inside circles on baking mats, making use of strain and leaving tip stationary till batter simply reaches fringe of circle. Transfer and elevate piping tip in a fast round movement as you end piping every macaron shell to stop some extent from forming on prime. Vigorously slam pans on counter 5 to 7 occasions to launch air bubbles. Sprinkle with hazelnuts. Let stand at room temperature till a pores and skin varieties on prime of macaron shells, 30 to 45 minutes. (Batter needs to be matte, really feel dry to the contact, and shouldn’t persist with your finger.)
Preheat oven to 300°F (150°C).
Bake till shells are agency however have a slight wobble to the contact, 13 to fifteen minutes. Let cool utterly on pans on wire racks.
Spoon Hazelnut-Chocolate Ganache right into a pastry bag fitted with a medium spherical piping tip (Ateco #804.) Pipe ganache onto flat facet of half of macaron shells. Frivolously press remaining macaron shells, flat facet down, on prime of ganache. Refrigerate in an hermetic container for as much as 3 days.
