Heat the butter in a large deep-sided skillet over medium heat. Once melted, add the bacon and cook until crispy, about 5 to 7 minutes, stirring occasionally. Use a slotted spoon to transfer the crisped bacon to a paper towel-lined plate to drain.
To the same skillet, add the onion, cabbage, garlic, salt, marjoram, black pepper, and water. Cook (covered) until the cabbage is tender, about 15 minutes, stirring occasionally. Add a splash of water if the pan starts to get too dry.
Add the flour and cook 1 minute, then add the milk and cook about 2 minutes more, stirring constantly. Turn off the heat and stir in the crisped bacon.
Transfer to a serving dish and top with the parsley, if using.
Notes
Low Carb and Keto Version: Omit the milk and flour. When the cabbage is tender, add 1 cup heavy whipping cream and bring to a simmer. Transfer to a serving dish and top with the parsley.
Paleo Version: Omit the flour and milk. Once the cabbage is tender, add 1 cup canned light coconut milk (or full-fat for a richer dish) and bring to a simmer. Transfer to a serving dish and top with the parsley.
To Make This a Full Meal for 4 People: Add 1 (16 oz/450 g) can rinsed and drained white beans when you add the milk.