I am in love with this flavor combination. I have made the Butterscotch Peanut Butter Cake and the Peanut Butter Marshmallow Butterscotch Pizza.
Over a double boiler (medium sauce pan with about an inch of water set to simmering and a bowl placed on top of the saucepan) pour in 1 bag of butterscotch chips and 1 tablespoon oil.
Stir occasionally until mostly melted and then remove from heat. (about 2 minutes) Continue to stir until all melted then pour butterscotch into a parchment lined 9x13 pan.
Gently pour marshmallows onto butterscotch and make sure they are evenly covering bottom.
Stir occasionally until mostly melted, remove from heat. You want to peanut butter chocolate mixture to be easily spreadable. (If it is not, add more oil in 1 teaspoon increments)
Remove butterscotch marshmallow mixture from freezer and pour peanut butter mixture over top. Using offset spatula, spread peanut butter mixture evenly over marshmallows.
When ready to serve, remove from refrigerator and lift up sides of parchment to dislodge from pan. Cut into chunks (using a knife works best) and serve at room temperature.