For the sauce:

1. In a small bowl, mix together soy sauce, brown sugar, sesame oil, fresh ground black pepper, and 3/4 of minced garlic. Set aside.

For the onion:

1. On a non-stick pan, add a teaspoon of oil and stir fry the onion. Add a pinch of salt to season the onion.
2. Stir fry with constant stirring, about 2-3 min. Set aside. 

For the carrot:

1. On the same pan, you cooked onion, add another teaspoon of oil, and stir fry the carrot.
2. Season with salt. Set aside.

For the mushroom:

1. On the same pan you cooked carrot, add the mushroom and cook for 3-4 minutes until it releases its water.
2. Add about a tablespoon of prepared Japchae sauce and stir fry for an additional minute or two. Set aside. 

For the spinach:

1. In a large bowl, prepare an ice bath.
2. Blanch the spinach for a minute or two. By using a skimmer or kitchen spider, get all the spinach out of boiling water.
3. Place them in the ice bath.
4. Drain and squeeze as much water out as possible.
5. In a bowl, add the blanched spinach, 2 teaspoons of sesame oil, the rest of the minced garlic (about half a clove), and salt to taste.
6. Mix well using your hand. Set aside. 

For Japchae:

1. Boil the noodle and cook for about 5-7 minutes. The noodle will soften and become slightly translucent.
2. Drain and rinse with cold water.
3. Add about 1 tablespoon of vegetable oil and mix it with the noodle. Using kitchen scissors, cut the noodle couple of times.
4. On a large pan, heat about 1/2 tablespoon of vegetable oil and add the noodle. With constant stirring, stir fry the noodle for 3-5 minutes.
5. Pour in the prepared sauce to the noodle. Continue to stir fry the noodle for additional 2 minutes until the noodle becomes almost translucent and cooked all the way (you can taste to see if it needs to be cooked a little longer). 
6. In a large bowl, transfer the noodle into the bowl with the rest of the ingredients. Mix until everything is well incorporated.
7. Garnish with sesame seeds. Enjoy.