Triple Chocolate Fudge

3 1/3 C sugar
1 C butter
1 C packed dark brown sugar
1 can (12 oz) evaporated milk
32 large marshmallows,  halved
2 cups (12 oz) semisweet chocolate chips
2 milk chocolate candy bars (7 oz each), broken
2 squares (1 oz each) semisweet baking chocolate, chopped
1 tsp. vanilla extract
2 C chopped pecans

In large saucepan, combine first four ingredients. Cook and stir over medium heat until sugar is dissolved. Bring to a rapid boil and boil for 5 minutes, stirring constantly. Remove from the heat and stir in marshmallows until melted. Stir in chocolate chips until melted. Add chocolate bars and baking chocolate and stir until melted. Fold in vanilla and pecans. Pour into a greased 15" x 10" x 1" baking pan. Chill until firm. Cut into squares.