Using the whisk on a hand mixer, combine the butter, cane sugar and treacle. Add the egg and continue to beat until the mixture becomes lighter in colour. Add the flour, cocoa, cinnamon, baking powder and salt. Flatten the dough a little, cover and chill for approx. 1 hour.
Roll out the dough in portions between two pieces of baking paper to a thickness of approx. 4 mm. Cut out squirrels.
Transfer the biscuits to a baking tray lined with baking paper. Place a hazelnut on each squirrel, press down, chill for approx. 15 mins.
Approx. 8 mins. in the centre of an oven preheated to 200°C.
Mix the egg white with as much icing sugar as it takes to produce a thick icing. Transfer the icing to a piping bag with a smooth nozzle (approx. 2 mm in diameter), pipe the eyes and stomach onto the squirrels, leave to dry. Transfer the melted chocolate to a piping bag with a smooth nozzle (approx. 2 mm in diameter). Pipe the tail and eyes, decorate with chocolate shavings.