The weight of the powdered sugar is key to this recipe. If you don't have a kitchen scale, scoop the powdered sugar into a dry measuring cup with a spoon and level it off for four and a half cups. If you use 16 ounces of powdered sugar you will get a fudge that is soft and requires refrigeration for cutting. If you use 18 ounces of powdered sugar you will get a fudge that sets but is very very sweet. 17 ounces is the sweet spot.