Prepare ingredients: Mince garlic, onion, and ginger. Peel and cube the potato into one-inch pieces.
Prepare the ribs: Cut the meat vertically along the bone, rinse, then lay with the meat side up. Cut horizontally to open like a book.
Parboil and slow-cook: Boil ribs for 5 minutes, drain, then return them to a pot. Add 1 litre of water, white vinegar, and beef stock. Slow-cook with the lid closed for 60 minutes, adding water as needed to keep submerged.
Make the sauce: Whisk gochugaru, gochujang, soy sauce, sesame oil, tomato paste, and black pepper in a bowl until combined.
Simmer: Add sauce, garlic, and onion to the ribs, stir, then add potatoes. Simmer on medium-low for 20-30 minutes, stirring every 3-5 minutes. In the last 10 minutes, reduce to low and stir continuously. Garnish with parsley and serve with steamed rice and kimchi.