Instructions

• Line an 8-inch square pan with aluminum foil, leaving an overhang on two sides; spray the foil with cooking spray and set the pan aside.
• In a large microwave-safe bowl, combine 1 heaping cup creamy peanut butter, ½ cup light corn syrup, ½ cup granulated sugar, and ¼ cup light brown sugar (packed).
• Microwave the mixture on high for 1 minute. Remove and stir; the mixture may still be granular. Return to the microwave and heat on high for 1 more minute.
• Stir in 1 tablespoon vanilla extract until combined.
• Add 3½ cups corn flakes to the peanut butter mixture and stir until the cereal is evenly coated.
• Turn the coated cereal mixture into the prepared pan. Press and pack it down somewhat firmly and evenly with a spatula, then smooth the top. Set the pan aside.
• In a large microwave-safe bowl (you may use the same bowl if scraped clean), combine ½ heaping cup semi-sweet chocolate chips and ¼ heaping cup creamy peanut butter (the peanut butter to be melted with the chocolate).
• Microwave the chocolate mixture on high for 1 minute. Stir; if the chips are not fully melted, return to the microwave in 10–15 second bursts, stirring between bursts, until the mixture is smooth.
• Pour the melted chocolate-peanut butter mixture over the cereal layer and smooth the top lightly with a spatula or knife.
• In a small microwave-safe bowl, heat ¼ cup creamy peanut butter (for swirling) about 30 seconds, then stir until smooth.
• Drizzle the melted peanut butter over the chocolate in five wide, evenly spaced, parallel lines that span the width of the pan.
• Rotate the pan 90 degrees. Using a toothpick or the tip of a knife, draw five evenly spaced lines perpendicular to the drizzled lines (starting at one side and dragging to the other) to create a marbled pattern.
• Cover the pan with a sheet of foil and refrigerate until the chocolate layer is completely set, at least 2–3 hours or overnight.
• Use the foil overhang to lift the set slab from the pan, place on a cutting board, and slice into bars. Serve.