Whisk together all ingredients in a jar with a tight-fitting lid (old jam jars work well).
Close and refrigerate for at least 4 hours, but preferably overnight before eating.
Notes
If you use plain yogurt, you might want to add a little bit of sweetener, like honey or syrup.Optional ingredients could be other fruit (fresh, frozen or canned), nuts, seeds, peanut butter, or seasonings like vanilla or cinnamon.