Preheat the oven to 190 degrees C. Grease a baking tray or line with baking paper.
In a large bowl, cream together the butter and caster sugar until smooth. Beat in the eggs one at a time. Stir in the vanilla and pumpkin puree until well blended. Combine the flour, baking soda, baking powder, salt, cinnamon and nutmeg; stir into the pumpkin mixture. Mix in the chocolate chips. Stir in the walnuts if desired. Drop by teaspoonfuls onto the prepared tray.
Bake for 12 to 15 minutes in the preheated oven, until edges begin to brown. Allow to cool for a few minutes on the tray before removing to wire racks to cool completely