Line a 13x9 inch pan with nonstick foil or parchment paper. For a half batch, use an 8-inch pan.
In a large (3 quart) nonstick saucepan, combine sugar and corn syrup and heat just until mixture begins to boil and sugar starts to dissolve. Remove from heat and stir in peanut butter and vanilla. Stir until well blended, then stir in the cereal.
Empty the mixture into the pan and press firmly. You may want to lay a piece of parchment or nonstick foil over the top to do this.
Place chocolate and butterscotch chips in a microwave-safe bowl or in a bowl set over simmering water. If using coconut oil or butter, add that too and stir it to coat the chips. The oil is optional and only if you want a softer topping.
If using the microwave, heat on 50% power for about 2 minutes, stirring every 30 seconds, until melted and smooth. If you are using coconut oil, I recommend covering the bowl very loosely with plastic wrap in case the coconut oil pops. This is usually only an issue if you are heating coconut oil by itself, but the loose cover is insurance.
.Spread melted chocolate mixture over top of bars and refrigerate until chocolate is slightly firm. If your ambient temperature is cool and you are not in a hurry, you can just let the chocolate set at room temperature.
When set, return to room temperature if you chilled (they are hard to cut when cold). Lift foil from pan and place on a cutting board. Cut into bars