Butter sides of a heavy 3-quart saucepan. In saucepan combine sugar, evaporated milk, and butter. Cook and stir over medium-high heat till mixture boils. Reduce heat to medium; continue cooking and stirring for 10 minutes.
Remove pan from heat. Add chocolate pieces, marshmallow creme, pecans and vanilla; stir until chocolate melts and mixture is combined. Beat by hand for 3 to 5 minutes or until mixture becomes very thick and starts to loose it gloss. Spread in the prepared pan. While fudge is warm, sprinkle with chopped candy bar. When fudge is firm, use foil to lift it out of pan. Cut fudge into squares. Store in a tightly covered container in the refrigerator. Makes about 4 pounds (96 pieces).