Make this easy snack in the microwave. Grease 13x9-inch pan with butter. Measure cereal into large bowl. Reserve 1 cup of the marshmallows. In large microwavable bowl, microwave remaining 4 1/2 cups marshmallows, the chocolate chips, butter, sugar and water uncovered on High 2 minutes to 3 minutes 30 seconds, stirring after every minute, until melted and smooth when stirred. Stir in vanilla. Continue as directed in recipe.
If you spray your bowl with cooking spray before using it, you'll have less mess to clean when you're done.
The sugar and water can be replaced with 1/4 cup corn syrup.
If you prefer your marshmallows more visible in the bars, just a wait a minute or two after mixing the warm chocolate and marshmallow mixture into the cereal to allow it to cool slightly before you stir in the final cup of marshmallows.