Our generation heard it from the singing of my mother's sister, Frances Byrne (nee Daly). I am unsure where she got it. We sang about scallions.

What's missing in this link is that Irish mothers would always put a sixpence wrapped in wax paper in the steaming hot dish. It certainly ensured that us kids would eat mountains of it. And we were only fed Colcannon once a year, on Oíche Samhna (Halloween).