Shulchan Arukh, Orach Chayim 508/שולחן ערוך·אורח חיים תק״ח

1Things forbidden on Yom Tov for preparing roasted food. Containing 2 paragraph):We do not heat stones to roast or bake upon them, because this hardens them. We do not break earthenware, and we do not cut paper to roast upon them. And we do not split a reed to make it like a spit for roasting.

2One may crack nuts with a cloth, and we are not concerned that it might tear.