Chocolate Hazelnut Macarons

Line 3 rimmed baking sheets with silicone macaron baking mats.

In the work bowl of a food processor, pulse flour, confectioners’ sugar, and cocoa until finely ground and fully combined. Sift mixture through a large fine-mesh sieve into a large bowl, discarding any solids. Add 2 egg whites (60 grams); fold until combined. Cover with plastic wrap to prevent drying out.

In a small saucepan, stir together granulated sugar and 1⁄4 cup (60 grams) water. Cook over high heat, without stirring, until an instant-read thermometer registers 240°F (116°C) to 245°F (118°C).

Meanwhile, in the bowl of a stand mixer fitted with the whisk attachment, beat cream of tartar and remaining 2 egg whites (60 grams) at low speed until foamy. Increase mixer speed to medium-high, and beat until medium-stiff peaks form. (Egg whites and sugar syrup should be prepared so they are ready at the same time.)

With mixer on high speed, add sugar syrup to whipped egg white mixture, carefully pouring straight into mixture, avoiding side of bowl and whisk. Beat until mixture is cooled and stiff peaks form, about 4 minutes.

Add one-fourth of meringue (about 1⁄2 cup or 60 grams) to flour mixture; stir vigorously until combined. Add remaining meringue, and carefully fold until mixture is ribbon-consistency. (Mixture should be thick and slowly but freely fall off the spatula in a “V” shape; when you drag the spatula through the batter, it should move like lava and slowly come back together.)

Transfer batter to a pastry bag fitted with a medium round piping tip (Ateco #804). Holding piping bag with opening of tip perpendicular to a prepared pan, pipe batter within circles on baking mats, applying pressure and leaving tip stationary until batter just reaches edge of circle. Move and lift piping tip in a quick circular motion as you finish piping each macaron shell to prevent a point from forming on top. Vigorously slam pans on counter 5 to 7 times to release air bubbles. Sprinkle with hazelnuts. Let stand at room temperature until a skin forms on top of macaron shells, 30 to 45 minutes. (Batter should be matte, feel dry to the touch, and should not stick to your finger.)

Preheat oven to 300°F (150°C).

Bake until shells are firm but have a slight wobble to the touch, 13 to 15 minutes. Let cool completely on pans on wire racks.

Spoon Hazelnut-Chocolate Ganache into a pastry bag fitted with a medium round piping tip (Ateco #804.) Pipe ganache onto flat side of half of macaron shells. Lightly press remaining macaron shells, flat side down, on top of ganache. Refrigerate in an airtight container for up to 3 days.

In a medium microwave-safe bowl, heat all ingredients on high in 30-second intervals, stirring between each, until butter is melted and mixture is smooth and well combined. Cover and let cool completely. Use immediately.