Prepare the Mixture:
In a large saucepan, combine the corn syrup and powdered sugar. Stir the mixture constantly over medium heat until it begins to boil.
Add the Peanut Butter:
Once the mixture has reached a boil, remove the saucepan from heat. Stir in the peanut butter and vanilla extract until the mixture is smooth and well combined.
Mix in the Cereal:
Gradually stir in the Rice Krispies cereal until the cereal is evenly coated with the peanut butter mixture.
Form the Balls:
Using a spoon, drop spoonfuls of the mixture onto silicone mats or waxed paper. Allow them to cool slightly, then roll each spoonful into a ball with your hands.
Cool and Serve:
Let the Rice Crispy Peanut Butter Balls cool completely before serving. Store them in an airtight container for up to a week.