This is a recipe for firm yogurt jelly that can be made simply by mixing and chilling. Mix yogurt with sugar and gelatin dissolved in the microwave, then return it to the original yogurt container and chill thoroughly in the refrigerator until firm. The key points are to bring the yogurt to room temperature to prevent lumps, not to boil the gelatin, and to mix without creating bubbles. This smooth and refreshing yogurt jelly is delicious on its own, or with jam on top if you like.