In a small saucepan over medium heat, bring sugar, butter and water to a boil. Remove from heat; stir in chocolate chips until melted. In a mixing bowl, beat eggs and vanilla. Add chocolate mixture; mix well. Combine flour, baking soda and salt; add to chocolate mixture. Stir in walnuts if desired. Pour into a greased 9 inch pie plate. Bake at 350 °F for 28 to 30 minutes or until brownie test done. Cool on a wire rack. For fudge sauce, heat chocolate chips, milk, sugar and butter in a microwave or double boiler until chocolate and butter are melted; stir until smooth. Drizzle some over pie. Cut into wedges; serve with ice cream and additional sauce.