Shabbos 3:2

If an oven (tanur, which is wide at the bottom and narrow above) is heated using straw or stubble as fuel, one may not put anything in it or on it. If a kupach (like a miniature kirah – like our ovens only smaller) is heated using straw or stubble as fuel, it is treated like a kirah (see Mishna 3:1); if it is heated using peat or wood, it's treated like a tanur.

Shabbos 3:3

One may not put an egg next to a boiler in order to partially cook it, nor may one crack an egg into a heated scarf, though Rabbi Yosi permits it. Nor may one bury an egg in hot sand in order to roast it.