Thinly slice 300g of boneless beef short ribs. Measure 4 teaspoons of sugar. Toss beef with half the sugar, 2 teaspoons of soy sauce and 2 teaspoons of minced garlic. Marinate for 15 minutes.
Mix ¼ cup of soy sauce, the remaining sugar, ½ teaspoon of minced garlic, and 1½ tablespoons of sesame oil in a large bowl. Cook 250g of dried sweet-potato noodles following the package directions. Drain, rinse briefly and add without mixing.
Measure 4 tablespoons of vegetable oil. Slice 1 onion, 200g of stemmed shiitake mushrooms, 2 carrots, and 1 red bell pepper. Cut 3 scallions into lengths, separating whites and greens.
Heat half the oil in a wide skillet over high heat. Stir-fry onion, mushrooms and scallion whites for 3 minutes. Transfer to the noodle bowl.
Heat half the remaining oil. Stir-fry carrot and pepper for 1½ minutes. Add 4½ packed cups of baby spinach and the scallion greens; stir-fry for 1½ minutes. Transfer to the bowl.
Heat the remaining oil. Stir-fry beef until just cooked through. Add to the bowl with 2 tablespoons of white sesame seeds. Toss everything together and season with salt and pepper.
