Preheat oven to 350 degrees F (175 degrees C). Spray a 9x13-inch baking dish with cooking spray.
Beat flour, sugar, butter, eggs, vanilla extract, baking powder, and salt together in a bowl; pour into prepared baking dish.
Bake in the preheated oven until golden, about 20 minutes. Pour marshmallows over the cake layer and return to oven; bake until the marshmallows puff, about 2 minutes more.
Stir peanut butter and butterscotch chips together in a saucepan over medium heat until melted; add crispy rice cereal. Spread peanut butter mixture over marshmallow layer; cool completely before cutting into bars.