Japchae (also spelled "chapchae") is a Korean dish that is based on slippery, resilient sweet potato noodles (sometimes mung bean noodles are used, but they have a more tender texture). Korean restaurants often serve it as part of the banchan (side dish) selection, but you can also serve it as an accompaniment to grilled meats, or even by itself, as a light meal. As with many Korean dishes, there's quite a bit of prep work involved but, once all the ingredients are ready, the cooking is quick and easy.
The dangmyeon (sweet potato noodles) and Korean zucchini (which has a milder flavour and smoother, more tender skin than Italian zucchini) are sold at shops specialising in Korean ingredients, where you can also pick up packets of beef short ribs cut for Korean barbecue, and the banchan. If you can't find Korean zucchini, substitute a yellow summer squash.
Prepare the beef and mushrooms. Soak the mushrooms in warm water until completely hydrated, about two to three hours. Squeeze out the water, then cut off and discard the stems. Thinly slice the caps and put the pieces in a small bowl.
Thinly slice the beef and put it in a small bowl. Stir 30ml (2tbsp) of soy sauce with 5g (1tsp) of sugar until the latter is dissolved. Mince the garlic and spring onion, then add them to the soy sauce mixture. Mix in the sesame oil, sesame seeds and ground white pepper. Divide the mixture evenly between the mushrooms and beef and mix thoroughly. Set aside to marinate while preparing the other ingredients.
Prepare the vegetables. Finely julienne the zucchini and carrot then put them in a bowl, sprinkle with two teaspoons of salt and mix well. Leave the vegetables for about 10 minutes, or until they soften. Rinse the zucchini and carrot together under cold, running water, pressing and massaging them to get rid of the excess salt. Drain the vegetables then lay them on a clean dish towel. Roll the towel around the vegetables to squeeze out as much water as possible.
Mince the garlic clove, then halve the onion and thinly slice it. Heat about 10ml (2tsp) of cooking oil in a 20cm (8in) skillet, add the onion and a light sprinkling of salt and cook over a medium flame until crisp-tender. Put the onion in a large bowl and wipe out the skillet with a paper towel. Heat about 5ml (1tsp) of cooking oil in the skillet, add the carrot, zucchini and minced garlic and sauté for about a minute. Put the vegetables in the bowl with the onion, then again wipe out the skillet with a paper towel. Heat about 5ml (1tsp) of oil in the skillet and add the mushrooms and their marinade. Cook over a medium-high flame until the mushroom pieces absorb the liquid. Put the mushrooms in the bowl with the other ingredients. Heat 5ml (1tsp) of oil in the skillet, add the beef and its marinade and cook over a medium-high flame until the beef is just cooked through. Add the beef to the bowl containing the other ingredients.
Bring a large pot of water to the boil and stir in 15ml (1tbsp) of cooking oil and 15ml (1tbsp) soy sauce. Add the sweet potato noodles and cook for about 3-5 minutes until tender but not mushy. Drain the noodles then rinse them for about a minute under cold running water, constantly massaging them with your hands. Drain again then drizzle 5ml (1tsp) of sesame oil over the noodles and mix well so they're lightly coated.
Whisk the egg thoroughly. Wash the skillet and dry it. Heat it over a medium flame, then brush it with cooking oil. Add about half the egg and swirl the pan so the egg makes a very thin layer. Leave it to cook until set, flip it over and briefly cook the other side. Slide the egg crepe out of the pan and repeat with the remaining egg. Stack the egg crepes and roll them into a cylinder. Finely julienne the egg crepes, then unroll the pieces and separate them.
Slice the remaining spring onion on the diagonal into 5mm (¼in) pieces. Put the cooked noodles into the bowl containing all the other ingredients, add half the egg crepe and mix thoroughly. Dissolve 10g (2tsp) of sugar in 20ml (4tsp) of soy sauce, then mix in 20ml (4tsp) of sesame oil. Pour the mixture over the ingredients in the bowl and mix well. Put the ingredients onto a serving dish and scatter the sliced spring onion over them. Top with the remaining egg crepe then sprinkle with sesame seeds. Serve immediately, with banchan of your choice, and grilled meats, if you wish.