15 cups popped popcorn (about 3/4 cup kernels)
Vegetable cooking spray
1 cup plus 2 Tbsp. firmly packed dark brown sugar
1/2 cup butter
1/2 cup dark corn syrup
1/4 teaspoon kosher salt
1 cup lightly salted dry-roasted peanuts
1 (10.5 oz.) package candy-coated peanut butter pieces (such as Reese's Pieces)
How to Make It
Preheat oven to 325°. Spread popcorn in an even layer on a lightly greased (with cooking spray) heavy-duty aluminum foil-lined 13- x 18-inch pan. Stir together brown sugar and next 3 ingredients in a small saucepan over medium-low heat; bring to a simmer, and simmer, stirring constantly, 1 minute. Pour over popcorn, and stir gently to coat.
Bake at 325° for 25 minutes, stirring every 5 minutes. Add peanuts during last 5 minutes. Remove from oven, and spread on lightly greased (with cooking spray) wax paper. Cool completely (about 20 minutes). Break apart large pieces, and stir in candy pieces. Store in an airtight container up to 1 week.
Cook kernels without oil in the microwave. Place 1/4 cup kernels in a 2 1/2-qt. microwave-safe bowl; completely cover bowl top with a microwave-safe plate. Cook at HIGH 3 to 4 minutes or until kernels have popped. Repeat with remaining kernels.