If you don't know what prune whip is, it is whipped egg whites, stewed mashed prunes, and powdered sugar. I just found a recipe at recipe source. It just says to bake. But it seems it should be in a hot water bath. What do you think? Would it hurt to do that if it isn't required? They also didn't mention anything about greasing the pan either.
It sounds horrid but it's really good with warm custard sauce. At least my grandmother's was.