for the meringue - 25 g Dutch-processed cocoa powder - 50 g powdered sugar - 2 egg whites, room temperature - 50 g sugar
for the mousse - 125 g bittersweet chocolate, chopped - 125 g unsalted butter, room temperature - 3 egg whites, room temperature - 15 g sugar - 1 1/2 egg yolks, room temperature, lightly beaten