1. Combine lemon juice with water in a small saucepan. Stir in the sugar.

2. Set saucepan over moderate heat. Bring to a boil, stirring constantly, then remove from heat and cool to room temperature.

3. Pour the lemon mixture into a shallow pan (an 8-inch square cake tin is ideal) and set it in your freezer.

4. The ice will be ready in 3 to 6 hours, depending on the efficiency of your freezer. Because of the high sugar content, this ice will usually be soft enough to serve, so you may as well make it in advance of the day you'll be needing it.