1. Make up the biscuit dough. Roll out the dough on a lightly floured surface until it is 3 mm (1/8 inch) thick. Use a 5 cm (2 inch) plain cookie cutter to stamp out rounds. Put them on 3 large, oiled baking sheets and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes until starting to brown around the edges. Leave to cool on a wire rack.
2. Make the filling. Put the butter, icing sugar and peppermint essence in a bowl and, using electric beaters, beat together until smooth. Use it to sandwich the biscuits together.
3. Make the icing. Put the chocolate in a bowl set over a pan of gently simmering water (do not allow the bowl to touch the water) and stir until melted. Put the biscuits, one at a time on a fork, dip each one into the melted chocolate and put it on a sheet of baking paper to set. Repeat with the remaining biscuits.