Fill the large plastic food storage bag half full of ice, and add the rock salt. Seal the bag.

Put milk, vanilla, and sugar into the small bag, and seal it.

Place the small plastic food storage bag inside the large one, and seal it again.

Hold both ends of the plastic food storage back and shake it back and forth until the mixture is ice cream, which takes about 5 minutes.

Take the small bag out of the big one and enjoy the ice cream!

Note: 1/2 cup makes one scoop. If you double the recipe it can get hard to mix because it gets pretty heavy but it can be done.