Place the butter, sugar, egg and salt in a bowl, mix using the whisk on a hand mixer until the mixture becomes lighter in colour. Mix the flour, gingerbread spice, baking powder and lemon zest, stir into the mixture, cover and chill for approx. 30 mins. Roll out the dough in batches between two sheets of baking paper to approx. 2 mm thick, cut out shapes.
Place the biscuits on two baking trays lined with baking paper.
Approx. 9 mins. in an oven preheated to 180 °C (convection). Remove from the oven, leave to cool on a cooling rack.
Bring the milk to the boil while stirring. Reduce the heat, add the chocolate and gingerbread spice, melt and stir until smooth. Serve the hot chocolate with the gingerbread biscuits.