1.Clean all the ingredients. Cut the 1 carrot into matchsticks. Thinly slice the 0.5 medium onion. Cut 3 ounces shiitake mushrooms into strips. Cut the 4 ounces beef into strips.
2.Combine sauce in a small bowl: 3.5 tbsp soy sauce, 3 tbsp sugar, 2 tbsp sesame oil, 2 tsp minced garlic, 1 tbsp roasted sesame seeds, and black pepper. Mix well until the sugar is dissolved.
3.In a large non-stick pan, bring about 5 cups of water to a boil, and cook the 7 ounces Korean potato starch noodles until completely translucent and soft (). Drain in a strainer and rinse under cold running water. Drain well. Cut with scissors. Transfer to a large mixing bowl. Mix well with 3 tablespoons of the prepared sauce.
4.Fill the same pan with 2 cups of water. When water boils, blanch the 6 ounces spinach only until wilted. Drain quickly and shock in cold water. Squeeze out water, run a knife through the squeezed spinach a couple of times, and lightly season with salt.
5.Add 0.5 tbsp oil to the skillet, and stir fry the noodles over medium to medium high heat, stirring frequently, until translucent and a bit sticky (). Transfer back to the mixing bowl.
6.Add 0.5 tbsp oil to the pan, and stir fry the carrot over medium high heat, sprinkling with a pinch of salt. Do the same with the onions. Combine with the noodles.
7.Add the mushrooms along with 2 tablespoons of the prepared sauce and cook. Transfer to the bowl with the noodles.
8.Add the spinach and the remaining sauce to the bowl with all other prepared ingredients. Toss well by hand. Adjust the seasoning to taste by adding a little more (start with 1/2 teaspoon) soy sauce and/or sugar as necessary.