Preheat the oven to 150C/300F (fan). Place a large casserole pan on the hob, add 1 tbsp of the oil and heat until very hot.

Season the pork with the salt and pepper and place in the pan with the hot oil. Seal on all sides.

Pour the stock over the pork.

Add in the onion, the whole carrot, celery, garlic and ginger.

Now add the mirin, soy sauce, gochujang, and the red chilli. Bring to the boil, then place a lid on the pan and place in the oven for 4 hours. NOTE: Check two or three times during cooking, and top up with a little boiling water if needed. You’ll need at least 1 litre of liquid left by the time the pork finishes cooking.

Take the pan out of the oven and place the pork on a chopping board. Remove and discard the layer of fat. Shred the pork using two forks.

Place a sieve over a large bowl and strain the cooking liquid. Throw the strained vegetables away and place the liquid back in the pan with the shredded pork. Leave on a low heat to keep warm.

Place the eggs in a small pan. Just cover with cold water. Bring to the boil, then simmer for 6 minutes.

Remove the eggs from the heat and place them in a bowl of cold water to stop the cooking process.

If you're using dried noodles, place the noodles in a pan of boiling water and boil for 5 minutes. Then drain, run under cold water (to stop them sticking) and put to one side.

Heat the remaining oil in a frying pan.

Add the leek, season with a pinch of salt and pepper then fry for 5 minutes, stirring a couple of times.

Push the leeks to one side of the pan and add the spinach to the pan. Allow to wilt for 1 minute.

Divide the noodles between four bowls. Top with the hot broth, shredded pork, leek, spinach and carrot matchsticks.

Carefully peel the two eggs and slice them in half. Place 2 halves in each bowl.

Garnish the soup with spring onions, then sprinkle with the white and black sesame seeds and the chilli flakes before serving.