Irish bacon with cabbage is the original, quintessential St. Patrick's Day dish. This version, which includes a mouthwatering parsley sauce, is from "Forgotten Skills of Cooking" by Darina Allen.
Place bacon in a large pot and add enough water to cover. Bring to a boil over medium-high heat. If bacon is very salty, a white froth will form on surface of water. In this case, discard water and start again. Repeat process until no froth forms on surface of water; drain.
Cover bacon with hot water. Cover pot and simmer until almost cooked through, about 1 hour.
Meanwhile, slice cabbage across the grain into thin shreds; rinse with cold water if necessary. Add the cabbage to pot with bacon and continue cooking 20 minutes more.
Remove bacon from pot; strain cabbage and transfer to a large bowl or serving platter. Add butter and season with pepper; toss to combine. Serve bacon and cabbage with parsley sauce and potatoes.