1Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9x13 inch baking pan.
2Melt butterscotch morsels and margarine in a large bowl in microwave. Stir the mixture well and let it cool to lukewarm.
3While the liquid mixture is cooling, mix flour, brown sugar, baking powder, salt, vanilla, and eggs into the butterscotch mixture; mix well. Fold in marshmallows and chocolate morsels.
4Spread batter into a lightly greased 9x13 inch pan.
5Bake 25 minutes. Be careful not to overcook.
Footnotes
Tip
Aluminum foil can be used to keep food moist, cook it evenly, and make clean-up easier.