Japchae

Gather all ingredients.

In a bowl, whisk together soy sauce, sugar, sesame oil, and garlic until the sugar is completely dissolved. Set this flavorful sauce aside.

Bring a large pot of lightly salted water to a rolling boil. Add the sweet potato noodles and cook, stirring occasionally, until they are cooked through but still slightly firm to the bite (al dente), approximately 6-7 minutes.

Rinse the cooked noodles under cold water to stop the cooking process and drain well. Transfer the noodles to a bowl, add 2 tablespoons of the prepared sauce, and toss thoroughly to coat.

Gently squeeze the beef under running water until the juices run clear. In a separate bowl, mix the beef with 1 tablespoon of the prepared sauce. Set aside to marinate, allowing the flavors to meld.

Bring a pot of water to a boil. Cook the spinach in the boiling water until it is just wilted, about 1 minute. Drain quickly and immediately transfer the spinach to a bowl of ice-cold water to halt further cooking. Squeeze out any excess water, place the spinach in a large bowl, and season to taste with salt and pepper.

Heat 1 teaspoon of vegetable oil in a large skillet over medium-high heat. Cook the sliced onion until it is fragrant and slightly crisp, about 1-2 minutes. Transfer the onion to the bowl with the spinach.

Add another 1 teaspoon of vegetable oil to the same skillet. Cook the sliced mushrooms in the hot oil until they are lightly browned but still firm, approximately 1-2 minutes. Add the mushrooms to the onion and spinach mixture.

Heat the remaining 1 teaspoon of vegetable oil in the skillet. Cook the carrot matchsticks in the hot oil until they are lightly browned but still crisp, about 1-2 minutes. Add the carrots to the bowl with the other vegetables.

In the same skillet, cook and stir the marinated beef strips until they are nicely browned, about 1-2 minutes. Add the cooked beef to the vegetable mixture.

Add the noodles to the same skillet and cook, stirring, until they are heated through, approximately 1-2 minutes. Add the noodle to the beef and vegetable mixture. Pour the remaining sauce over the beef-noodle mixture and toss everything together using your hands to ensure an even coating.