Melt 5 cups marshmallows (reserve 1 c. From bag), chocolate chips, butter and corn syrup in 3 qt. Saucepan over low heat, stirring occasionally. Remove from heat; stir in vanilla. Grease a 13"x9"x2" pan.

Pour cereal into large mixing bowl. Pour marshmallow mixture over cereal; stir until evenly coated. Stir in remaining marshmallows.

Press mixture into prepared pan with buttered back of spoon. Cool until as firm as you'd like. Cut into bars. Store covered loosely at room temperature.