Melt the butter in a large skillet. Saute the onion and Brussels sprouts until the onion is soft and translucent. Add the corned beef and potatoes. Saute until warmed through. Season.
Okay, I really used Brussels sprouts and not "baby cabbage" (if there is such a thing) but I had to go with the theme! This is a great recipe for using up leftovers or cooking once, eating twice. I was making potato salad to eat later the same day so I just boiled up a ton of potatoes at once and chilled the rest until later.It is a tiny bit more involved than regular hash (chopping up the Brussels sprouts and all that) but I like it a lot better and with the addition of vegetables, can serve as a complete meal. I had it for an early lunch one day and it was perfect.