Preheat the oven to 155'C.
Sift the ground almonds, the icing sugar and the cocoa powder together.
Whisk the egg whites until fluffy, then add the caster sugar to the egg whites and continue whisking until you have stiff, glossy peaks.
Fold the ground almonds and icing sugar into the meringue mixture.
Cut and fold the mixture with a spatula until all of the dry ingredients are incorporated and the mixture is smooth, shiny and has reached the ribbon stage.
Spoon the mixture into a piping bag.
Pipe 2cm circles in straight lines across a baking sheet lined with a silicon paper. Leave a 1 cm gap between each macaroon shell. Drop the tray of macaroons onto the work surface from about 30 cm to remove any large air bubbles.
Allow the macaroons to rest at room temperature for 20 minutes or until the macaroon shells are no longer sticky to touch.
Bake in the oven for 15 minutes. If you are baking lots of macaroons you may need to keep the oven door slightly ajar (with a spoon or paper) to prevent steam building up in the oven. After 15 minutes, check the macaroons are cooked by gently lifting a macaroon at the edge of a tray. If the test macaroon does not stick, allow the tray of macaroons to finish cooking on the tray as it cools.
Allow the macaroons to cool completely before filling.
Bring the double cream up to the boil.
Once the cream has boiled, remove from the heat and pour over the chocolate. Leave the chocolate to rest for two minutes before stirring into a smooth and shiny ganache.
Zest and juice the orange and add to the still warm chocolate ganache.
Allow to cool at room temperature until set.
Spoon the ganache into a piping bag and then pipe on to the centre of half of the macaroon shells. Top with a second macaroon shell and twist gently to spread the mixture to the edges.
«Although a ganache can be refrigerated in order to cool it down more quickly, taking the time to leave it set at room temperature will ensure that it does not set rock-hard in the refrigerator.»