Japchae literally translated means "mixed vegetables." But the main ingredient of this classic dish is Korean sweet potato starch noodles (dangmyeon), also known as glass noodles. The chewy and springy noodles are well balanced with thin strips of cooked vegetables (typically carrots, spinach, onions, shiitake mushrooms, cucumbers, and bell peppers) and beef.
All of the ingredients, separately cooked to develop the layers of flavor, are combined at the end into a delicious and colorful dish. This classic method is what makes this dish special and a Korean favorite for special occasions and traditional holidays. Serve it as a first course or side dish or over a bed of rice to make it a main dish.
Note: Leftover japchae should be kept refrigerated. Japchae reheats well in the microwave. The noodles will get soft and chewy again.
*Note: Dried shiitake is ideal for its concentrated flavor and meatier texture, but you can use any kind of fresh or dried mushrooms such as oyster or button mushrooms.
Combine all of the ingredients and mix well until the sugar is dissolved. Set aside.
Cook the starch noodles according to the package directions. Rinse in cold water and drain. Cut the noodles with kitchen shears or a knife into 6- to 7-inch lengths. Place in a bowl, mix in 2 tablespoons of the prepared sauce, and set aside.
In a bowl, mix the beef with 1 tablespoon of the sauce. In another bowl, do the same with the mushrooms. Bring a small pot of water to boil over high heat, and blanch the spinach in boiling water only until wilted. Drain quickly and shock in cold water. Squeeze out excess water, cut into about 2-inch lengths, and lightly season with salt and pepper.
In a lightly oiled nonstick skillet, sauté each remaining vegetable separately with 1 teaspoon oil over medium-high heat for about 1-2 minutes. Season lightly with salt and pepper. (Do not overcook. The vegetables should be crisp.) With the remaining oil, sauté the beef for about 1-2 minutes. Transfer to a large bowl. Reduce heat to medium and sauté the noodles, stirring frequently, until translucent and sticky, about 3-4 minutes.
Combine all of the ingredients and the remaining sauce. Toss well, preferably by hand. Add more soy sauce and/or sugar, to taste.