If someone cooks meat and milk together at a very high temperature, so that they will be burned to ash, in the time that it takes from getting the ingredients to a hot temperature to the point that they are ash, does this constitute cooking as far as the Isur is concerned with cooking meat and milk together?
The Chasam Sofer (Y.D. Siman 92) writes that the prohibition of cooking meat and milk together is on the act of cooking, not the outcome. This is in contrast to cooking on Shabbos, which (according to him) is only forbidden if the object being cooking remains in the world. Based on this he explains the ruling of the Meil Tzedoka (Kanfei Yonan Siman 87) that candles manufactured with butter and animal fats are considered basar b’chalav and may not be lit as this is considered bishul; although the act of cooking destroys the basar b’chalav it is nonetheless included in the prohibition.