Grease 9" square pan (or similar) with butter or margarine and set aside
Place sugar, butter and evaporated milk in large heavy saucepan
Bring to a full rolling boil on medium heat, stirring constantly
Boil 4 min. or until candy thermometer reaches 234°, stirring constantly to prevent scorching. Remove from heat.
Add chocolate and marshmallow creme; stir until completely melted
Add walnuts and vanilla; mix well. Pour immediately into prepared pan; spread to evenly cover bottom of pan.
Cool at room temperature at least 4 hours
Cut into 1" squares. Store in tightly covered container at room temperature