Pour the eggnog into a 13x9-inch casserole dish or a cookie sheet. Place it into the freezer.
Every 30 minutes, stir and scrape the mixture with a fork, being sure to break up any frozen pieces around the sides. Freeze for a total of 4 hours.
Once the mixture is completely frozen and fluffed (it should look like snow) place it into a plastic container and keep for a few weeks.