Cut the kimchi into bite-size portions and place in a pot with the brine, sliced onions and two coarsely chopped spring onions. Add the salt, sugar, pepper flakes and pepper paste. Drizzle the sesame oil over and add the beef stock. Don’t stir or combine, just add it to the pot. Cover with a lid and cook for 10 minutes at a medium to high heat. Reduce the heat, add the diced tofu to the top of the stew and cook with the lid on for a further 10 to 15 minutes at a medium heat. Chop the last spring onion and sprinkle over the stew. Serve with rice.