In a medium saucepan, boil diced potatoes in salted water until fork tender. Pour into colander to drain. While the pot is till hot, add the 4 TBS butter and melt over low heat. Add the cabbage, scallion, salt and pepper to taste. Cook over medium heat until the cabbage is tender but still a bit crunchy. While the cabbage is cooking use a fork or potato masher to smash the potatoes, leaving some lumps. Pour the hot cabbage mixture into the potatoes and stir to combine. Add cream until you reach the desired consistency. Return to pot and reheat if necessary. Serve with a well in the center to hold a pat of butter. Season with salt and pepper.