Cook the noodles following pack instructions, then drain and rinse under cold water. Mix the ingredients for the japchae sauce together and set aside.

Mix the ingredients for the beef marinade together along with 1/2 tsp ground black pepper. Tip the beef into the marinade and ensure everything is thoroughly mixed. Set aside for 10 mins to marinate.

Place the spinach in a large heatproof bowl and cover with boiling water. Wilt for 1 min. Drain the spinach and rinse under cold water. Squeeze out any excess water. Place the drained spinach in a bowl along with the remaining spinach ingredients and 1/4 tsp salt and mix. Set to one side.

Crack the egg into a small bowl and stir with a fork. Place a small frying pan over a medium heat and heat the vegetable oil. Pour in the egg with a pinch of salt and move the pan around to coat it with a thin layer of the egg. Fry for 30 seconds, then flip and cook on the second side for 30 seconds to create a very thin omelette. Remove from the pan to cool, then roll into a tube shape to make it easier to slice. Slice the egg into thin strips, around 0.5cm thick. Set aside.

In a large frying pan, heat 1 tbsp vegetable oil over a medium heat. Using a pair of tongs, place the beef in the frying pan and fry for 1-2 mins. Remove the beef and set aside. Wipe the pan clean using kitchen paper and add 1 tsp more oil. Tip in the carrots with a pinch of salt and fry for 2 mins until slightly softened. Remove from the pan, wipe with a paper towel and add another tablespoon of oil. Fry the peppers for 2-3 mins until soft, remove from the pan, wipe clean and add another tablespoon of oil before frying the mushrooms for 6-8 mins until soft and golden.

Wipe out the pan and keep it on medium heat. Pour in 2 tbsp vegetable oil and when hot tip in the noodles to the pan and toss with a pair of tongs for 2 mins to heat through. Once the noodles are heated through, pour in the japchae sauce and all the other prepared ingredients, including the spring onions. Toss the ingredients together over a high heat for a further 2 mins, making sure everything is well combined and coated with the sauce. Serve immediately with some sesame seeds sprinkled over.