In a large bowl, measure cereal.

Butter 13x9-inch pan.

In large microwavable bowl, microwave 5 cups marshmallows, the chocolate chips, corn syrup and butter, uncovered on High for 2 to 3 1/2 minutes, stirring after every minute, until melted and smooth when stirred. Stir in vanilla.

Pour over cereal; quickly toss until completely coated.

Stir in 1 cup marshmallows.

Press mixture evenly in pan, using buttered back of spoon.

Let stand uncovered at least 1 hour, or refrigerate if you prefer a firmer bar.

For bars, cut into 6 rows by 4 rows.

Store loosely covered at room temperature up to 2 days.