Shabbat: Cooking by Solar Heat

You may cook or reheat food on Shabbat using solar heat, but only if the sun's rays directly cook the food. Practically, this can probably only be done by using a magnifying glass.
Note You may even cook or reheat liquids this way on Shabbat.
Note You may not cook the food by having the sun's rays first heat a surface—such as heating a black backing that will absorb heat--and then transfer it to the food.