Preheat the oven to 155'C.
Whisk the egg whites and 150g caster sugar until you have a stiff and glossy meringue mixture.
Place the icing sugar and the ground almonds in a blender. Blitz and then sieve this mixture into a bowl to ensure that you have a very fine, lump-free powder.
Incorporate the dry ingredients into the meringue mixture. Use a spatula to cut and fold the mixture until is smooth, shiny and ribbon-like.
Fill a piping bag with the macaroon mix and pipe the macaroons onto a lined baking tray. Leave the macaroons to dry slightly for 15 minutes at room temperature and then bake for 15-20 minutes.
Place the cream in a pan and bring to the boil.
Once boiling, pour it over the chocolate (broken in to small pieces) and then stir slowly so that the chocolate melts.
Allow the chocolate ganache to cool for 15-20 minutes.
In the meantime, peel the mandarin and cut the segments in to small pieces.
Pipe the chocolate ganache onto half the macaroon shells. Add a few mandarin pieces and top with a second macaroon shell.
Dust with cocoa powder before serving.
«To cool the filling for your macaroons more quickly, place the filling in a bowl and cool down whilst stirring over a bowl of ice.»