Blend the ground almonds and icing sugar in a food processor until well combined. Set aside.
Using an electric whisk, slowly whisk the egg whites in a large bowl at a low speed until stiff peaks form when the whisk is removed. Slowly whisk in the cream of tartar and caster sugar until the mixture is smooth and glossy, increasing the speed of the whisk as the mixture stiffens.
Gently fold in the food colouring and blended ground almonds and icing sugar until the mixture resembles shaving foam.
Spoon the macaroon mixture into a piping bag fitted with a 1cm/½in round nozzle. Pipe 5cm/2in circles onto the baking tray lined with greaseproof paper. If a peak forms, wet your finger and smooth it down. Sharply tap the bottom of the tray to release any air bubbles from the macaroons, then set aside for 60 minutes (the macaroon shells are ready to go in the oven when they are no longer sticky to the touch).
Meanwhile, preheat the oven to 160C/315F/Gas 2½.
Bake the macaroons in the oven for 10-15 minutes, or until cooked through. Remove from the oven and set aside to cool for 5 minutes. Carefully peel away the greaseproof paper and set aside to cool completely.
Meanwhile, for the chocolate filling, heat the double cream and chocolate in a saucepan over a low heat, stirring occasionally, until smooth and well combined. Add the brandy and butter and stir until smooth, then remove from the heat and set aside to cool completely.
Use the filling to sandwich the macaroons together then chill in the fridge for 30 minutes.