Preheat oven to 180'c. Beat butter and sugar until light and creamy. Add vanilla and continue to beat. Add the flour and baking powder, mix on low speed till combined. Add chocolate chips and mix together with you hands.
Press mixture into a lined square tin and bake for 15 minutes or until baked.
Pour caramel into a bowl and stir till smooth, may need to beat or whisk. Pour over the cooked base. Sprinkle marshmallows over the caramel and return to the oven for a further 5-10 min or until marshmallows are toasted.
Leave for at least 4 hours in the fridge to cool, preferably over night. Cut into small squares.