Prepare an 8-inch square baking pan by spraying with cooking spray and lining with parchment paper.
In a glass bowl in the microwave, melt butterscotch chips and peanut butter together until smooth, stirring in between.
Stir in the vanilla and pinch of salt and allow the mixture to cool to room temperature.
Once cooled, stir in marshmallows and mix till combined.
Pour mixture into prepared pan and refrigerate until set (about 2 hours).
Cut chilled bars into squares and serve.