Heat the oil over medium to medium-high heat in a 5-quart pot. When the oil starts to ripple, add the beef and cook until browned on both sides, about 5 minutes (cook in batches if necessary to avoid crowding the pot).
Add the cabbage, onion, Guinness, beef stock, bay leaves, marjoram, salt, and pepper. Bring the soup up to a boil, then cover it, turn it down to a simmer, and cook until the meat is tender, about 60 to 90 minutes, stirring occasionally.
Add the carrots, parsnips, celery, and potato, and bring the soup up to a boil. Turn it down to a simmer, cover it, and cook until the veggies and meat are tender, about 20 to 30 minutes, stirring occasionally.
In a small bowl, mix together the butter and flour until completely combined. Whisk this mixture (called a beurre manié) into the stew to thicken it.
Season to taste with additional salt and pepper.
Serve this stew garnished with fresh minced parsley along with Irish Brown Soda Bread.