Vanilla custard is suprisingly very varied in form. You can serve it with caramel sauce on top, in the classic Mexican flan. Or how about pairing the sweet vanilla flavor with raspberries? Try serving vanilla custard pie at your next brunch or take a cue from Guam and serve vanilla custard cake instead. Or how about serving the vanilla custard in individual cups?
Food Timeline provides us with some history on custard, but there doesn't seem to be a way to pinpoint when vanilla became a popular custard flavor.
Well, no way yet with current techology. I seriously doubt anyone has a working TARDIS.