Movies were men get turned into women?

There is a French Horror movie (I do not know the name) where this teenage looking guy is taken captive by this coven of witches. He is tied to a stake and his clothes and underwear are cut off. When he is naked, they cut off his male parts, rub him with some kind of red paste and smoke appears all around him. When it clears off he is a blonde haired naked woman. They do this to several guys, lots of nudity and blood.