2–3 lbs. potatoes (approx. 6–9), like Yukon Gold 1 small spring or Savoy cabbage 1 cup plus 1 tbsp. boiling milk Salt and freshly ground pepper, to taste ¼ cup butter
1. Scrub the potatoes. Put them into a saucepan of cold water, add a good pinch of salt, and bring to a boil. When the potatoes are about half cooked (about 15 minutes for old potatoes), strain off two-thirds of the water. Replace the lid on the saucepan, put on a gentle heat, and let the potatoes steam until they are fully cooked.
2. Remove the dark outer leaves from the cabbage. Wash the rest and cut into quarters, remove the core, and cut each quarter finely across the grain. Cook in a little boiling salted water until soft. Drain, season with salt, freshly ground pepper, and a little butter.
3. When the potatoes are just cooked, put on the milk and bring to a boil. Pull the skin off the potatoes, mash quickly while they are still warm, and beat in enough boiling milk to make a fluffy purée. (If you have a large quantity, put the potatoes in the bowl of a food mixer and beat with the paddle.)
4. Stir in about the same volume of cooked cabbage and taste for seasoning. Serve immediately in a hot dish, with a lump of butter melting in the center.
Note: Colcannon may be prepared ahead and reheated later in a moderate oven at 350°F, for about 20–25 minutes. Any leftover colcannon may be formed into potato cakes and fried in bacon fat until crisp and brown on both sides—a cousin of bubble and squeak.