Preheat the oven to 175°C (340°F/Gas 4). Grind the chicken with the stock and the butter in the food processor. Add the flour and cornflour. Knead the dough into a firm ball. Roll into a thin sheet on a flour-dusted countertop. Cut out shapes or cut into cubes. Bake until golden brown for 20 minutes. Leave to cool and keep in an airtight jar.