Add the vegetable oil to a pan (or the slow cooker if it can saute) and brown the beef ribs on all sides. Remove the ribs once browned and add the onion and cook for 5 minutes until soft and golden and then add the garlic for another 2 minutes.
Add the ribs, onions and garlic (as well as the cooking oil) to the slow cooker along with the ginger, beef stock, soy sauce, sugar, vinegar, gochujang and sesame oil. Cover and cook on a high heat for 6 hours.
Mix 8 tablespoons of the cooking liquid with the cornstarch in a bowl until smooth and then add back into slow cooker, stir to blend and then leave to cook uncovered on high for another hour.
Plate up with rice and kimchi, scatter over the sesame seeds and spring onions and serve.