Place potatoes in a large pot or saucepan with enough water to cover them. Bring to a boil, and cook for about 15 to 20 minutes or until tender.

Meanwhile, cook bacon in a large, deep skillet over medium heat until browned. Drain the bacon on paper towels and reserve the drippings. Crumble the drained bacon. Set bacon aside.

Saute the onion and cabbage in the reserved bacon drippings until translucent and tender. Covering is optional, but it will help the vegetables cook faster.

Drain the boiled potatoes, add back to the pot and mash them with milk. Season to taste with salt and pepper. Fold in the cabbage, onion and bacon, and then transfer to a serving bowl.

Make a well in the center of the mixture, pour in the melted butter, and serve immediately.