In a large saucepan, combine sugar and corn syrup. Cook over medium heat, stirring constantly, until the sugar is dissolved and the mixture comes to a boil.
Remove from heat and stir in peanut butter and vanilla until smooth.
Add Rice Krispies cereal and stir until well coated.
Press mixture into a greased 9x13 inch pan.
In a microwave-safe bowl, melt chocolate chips and butterscotch chips together in 30-second intervals, stirring in between, until smooth.
Spread the melted chocolate mixture evenly over the cereal mixture.
Let stand until set, or refrigerate for faster setting.
Cut into squares and serve.
Notes
Store in an airtight container at room temperature.