Shabbat 39 - Cooking in the sun
Not only it is forbidden to cook on Shabbat, but even when one takes the kettle off the stove, he should not put an egg next to the kettle, in order that it should get slightly cooked.
On the other hand, if one spread out cloth in the sun, he may try to fry eggs there, and, being that this is not a normal way of cooking with fire, it should be allowed. Nevertheless, the author of this ruling (usually the anonymous author is Rabbi Meir) forbids it - and Rabbi Yose allows it. What are their reasons? Both agree that cooking with fire derivatives (kettle) is forbidden. Both also agree that cooking in the sun is allowed, since this is unusual, and one cannot derive any wrong lessons seeing that someone cooks food in the rays of sun on Shabbat. Where they disagree is cooking with the derivatives of the heat of the sun (cloth spread out in the sun). Rabbi Meir says that it is forbidden, so that one should not come to cook with the kettle taken off the fire, while Rabbi Yose says that no one will confuse it, and therefore the additional prohibitions are unneeded.
Theodule Augustine Ribot - Still Life With Jugs And Eggs