Place popcorn in a large bowl; set aside. In a saucepan over medium heat, bring sugar and corn syrup to a boil, stirring constantly. Boil for 1 minute. Remove from the heat.

Stir in peanut butter and vanilla; mix well. Pour over popcorn and mix until well coated. Press into a buttered 19x9-in. pan. Sprinkle with mini M&M's Cool slightly before cutting. I cut mine into 1"x3" bars and it made about 2 dozen bars