Very vieux chapeau.... They were probably the 1960s equivalent of the wrought iron casserole dish in the wedding present popularity stakes.

The "Waterless Cooker" was a 1920s equivalent that used stacked internal dividers for steaming food without mixing flavours. They were still turning up, more or less complete, in junk shops and charity shops in the 1970s - admittedly we used ours mostly for boiling up wort.