Preheat the oven to 180ºC . Grease a 9 X 13 X 5 cm baking pan. Melt the chocolate in the top of a double boiler and set aside. Mix the sugars, corn syrup and butter together but do not cream. Add the eggs, one at a time. Slowly pour in the chocolate, blending well. Add the flour, beating until smooth. Fold in the walnuts. Spread the batter in the prepared pan and bake for 25 to 30 minutes. Place the pan on a wire rack and allow to cool completely before cutting into squares. Yield: 24 Brownies