In a food processor, blitz the almonds with all the other ingredients up to and including the cocoa powder.
Beat the egg whites with the salt until stiff. Add the reserved sugar and continue beating until the egg whites turn glossy. Sieve the almond mixture over the egg whites and carefully stir in. Transfer the mixture to a piping bag with a smooth nozzle (approx. 9 mm in diameter), pipe approx. 60 small mounds (each approx. 2.5 cm in diameter) onto two baking trays lined with baking paper. Gently flatten the peaks a with a wet finger.
Approx. 18 mins. in an oven preheated to 130 °C (convection). Remove from the oven, allow to cool slightly, then leave to cool completely on a rack.
Beat the butter, sugar, gingerbread spice and fleur de sel for approx. 2 mins. using the whisk on a hand mixer. Spoon the butter cream into a piping bag with a smooth nozzle (approx. 9 mm in diameter). Turn over half of the macarons, pipe a little filling on each. Place the remaining macarons on top, press down gently, cover and chill for approx. 1 hr.