Place potatoes in a 5 to 6 quart pan with water. Cover and bring to a boil over high heat. Reduce heat; simmer until tender when pierced, about 15 minutes. Drain potatoes; mash, part at a time, in a heavy-duty mixer or by hand in a large bowl. Place cabbage and butter in a pan, cover and steam over medium-high heat until well wilted, stirring often. Stir milk and onions in a 3 to 4 quart pan over medium heat until simmering. Pour milk mixture into potatoes. Stir. Stir in cabbage. Season with salt and pepper. Stephanie de Silva at GAELIC-L recipe archive.