In a bowl, cream the butter and the sugars together. Add the vanilla, egg and Christmas Cake & Pudding Spice, and beat until it has the consistency of a heavy mousse, then gently knead in flour and baking soda.
When a smooth and thick dough forms, add the walnuts. Pick off pieces of dough and roll into walnut-sized balls. Place them on a parchment-lined baking sheet.
Bake for 8 minutes or until the cookie edges are golden.