1. Chop Onions, mix with milk and heat until tender, near boiling, set aside to infuse.
2. Boil whole potatoes in jackets until tender, leave in hot water off the heat until you get your cabbage cooking.
3. Remove outer leaves from cabbage, rinse, cut in quarters, remove core. Slice the quarters into narrow strips. Place in skillet with 3-4 Tbsp butter, salt and pepper, cover. Cook over medium heat until it JUST starts to brown. Stir occasionally. OR You can boil and drain the cabbage if you rather.
4. Remove potato skins, discard. Place whole peeled potatoes in large bowl(use stand mixer if you have one). Beat while still hot, with as much of the milk, and the onions as it takes to make them fluffy. Add butter, salt and pepper to taste and the cooked cabbage. Blend until well mixed. Move to serving dish, top with about two tablespoons butter.
Serve with any meat, such as corned beef brisket or roast beef.
Leftovers can be shaped into patties and fried for breakfast, then, it's called Boxty.