Cook the potatoes. Place potatoes in a saucepan and cover with water. Bring to a boil and cook for 15 to 20 minutes, or until tender.
Cook the bacon. Place bacon in a large, deep skillet. Cook over medium high heat until evenly brown. Drain, reserving drippings, crumble and set aside.
Cook the cabbage. In the reserved drippings, saute the cabbage and onion until soft and translucent. Putting a lid on the pan helps the vegetables cook faster.
Mash and mix the potatoes. Drain the cooked potatoes, mash with milk and season with salt and pepper. Fold in the bacon, cabbage, and onions, then transfer the mixture to a large serving bowl.
Top it all off with butter. Make a well in the center, and pour in the melted butter. Serve immediately.
