In a large saucepan, combine corn syrup and powdered sugar. Stir continuously over medium heat until it comes to a rolling boil, about 3–5 minutes. Remove from heat immediately.

Quickly stir in chunky peanut butter and vanilla extract with a wooden spoon until smooth and well combined.

Gently fold in Rice Krispies cereal, ensuring every piece is evenly coated, about 1-2 minutes.

Line a baking sheet with wax paper or silicone mats. Drop spoonfuls of the mixture onto the surface and allow to cool for 10-15 minutes before shaping into balls.

Once cool, roll each scoop into a smooth ball or press mixture into a greased pan to create bars. Allow to set for about 30 minutes.