1. This is very similar to the bag method, except instead of using two bags, you use two coffee cans, one bigger than the other.
2. Put the ice cream mixture in the smaller coffee can. Seal tightly.
3. Put the smaller coffee can in the big coffee can along with ice and rock salt. Seal the large can tightly.
4. Shake the large can vigorously for about 10 minutes. Kids can roll or throw it around, but make sure the cans are sealed well. Do this step outside, just in case. Check the smaller coffee can to see if the mixture has turned into ice cream yet. If you see ice crystals forming, stir or whisk the mixture.