1. To make the meringue shells, mix the almonds, icing sugar and cocoa in a bowl, then grind very finely in batches in a food processor or blender. Pass this mixture through a fine-meshed sieve. Beat the egg white with the salt and lemon juice until stiff. Slowly add the sugar, and continue to beat the egg white until it is firm enough to cut. Stir the almond mixture into the beaten egg white in three portions, pressing some of the air out with the back of the spoon as you do so. This should create a thick, homogeneous batter.
2. Add the mixture to a piping bag with a medium-sized nozzle. Pipe 40 equal-sized dollops (about 3 cm/1¼-in in diameter) onto a baking sheet lined with baking parchment, leaving spaces between them. Once all the macarons have been piped out, tap the bottom of the baking sheet with your hand a few times. Leave to dry for 20–30 minutes at room temperature.
3. Preheat the oven to 140°C (280°F/gas 3). Bake the macarons for 14 minutes. Carefully remove the baking parchment together with the macarons from the baking sheet and allow to cool, and only then remove them from the parchment.
4. To make the filling, break the chocolate into pieces, and heat with the cream in a small saucepan over a medium heat until it has melted. Whisk the butter in well. The chocolate buttercream should now be spreadable—otherwise, put it in the fridge for a short while. Add the cream to a piping bag with a small nozzle and pipe onto half of the meringue shells. Top with the remaining shells.

Recipe reprinted with permission from Hardie Grant Books.