Well, the expression definitely exists in this area -- and not only in my dream.
I have had time to think more about it, and I assume it is related to "You had better..." as in "You had better eat". That, of course, could become "You'd better eat", and I THINK it could become "You better had..."
That's the way I see it, and I admit to having used 'You better had', but with a degree of self-awareness. (It may be archaic. It's certainly arch. )