Julia Child did some 400° cooking, for a science-oriented TV series called “The Ring of Truth”: www.youtube.com/watch?v=WQ3mjb9BSaU&t=850s
Later in the episode, she got to cook a diamond to amorphous carbon. “I’ll remember that recipe – one carat diamond, two and a half hours, three thousand degrees”: www.youtube.com/watch?v=WQ3mjb9BSaU&t=1458s