From Fine Cooking #131, p. 91
In some of our make-ahead holiday sides, some components get frozen in zip-top freezer bags. Especially for sauces, it’s best to freeze the contents flat, as shown here. Not only will they stack more neatly in your freezer, but they’ll also thaw quicker because they’re so thin. When freezing liquids, lay the bag flat while holding the zip-top end up a bit so that the liquid stays in the bag. Force out as much air as you can, seal the bag tightly, then freeze it on a flat surface, preferably a tray to catch any leaks.