PREHEAT oven to 300° F. Spray large roasting pan and large, foil-lined rimmed baking sheet with nonstick cooking spray. Place popcorn and peanuts in prepared roasting pan. Set aside prepared baking sheet for use later.
COMBINE morsels, corn syrup and butter in medium, heavy-duty saucepan. Cook over medium heat, stirring constantly, until mixture boils. Immediately pour over popcorn mixture in roasting pan; toss well to coat.
BAKE, stirring every 10 minutes, for 40 to 45 minutes. Place prepared baking sheet on wire rack. Carefully pour mixture onto baking sheet and spread evenly. As mixture cools, it will harden. Once completely cool, break into bite-size pieces. Store in airtight container. Makes about 14 cups.