Preheat oven to 170 degrees. Brush a 1 litre oven proof dish with melted butter. Place the sugar, flour, baking powder and walnuts in a food processor and process for a few seconds. Add milk, egg, remaining butter, golden syrup and vanilla and process until just combined. Spread the mixture into the baking dish.
To make sauce, combine sugar and cornflour in a bowl. Sprinkle over sponge mixture. Mix golden syrup with ¾ cup of hot water and pour over the top. Bake for 35 – 40 minutes or until skewer comes out clean when tested.
Stand for 5 minutes then serve with cream or ice cream garnished with walnuts.