1: In a large bowl, whisk together cornstarch, baking powder, salt, black pepper, oyster sauce, soy sauce, and vegetable oil.
2: Add the sliced beef and mix until coated. Cover and refrigerate for at least 30 minutes or overnight.
3: In a bowl, whisk together light soy sauce, dark soy sauce, ketchup, sesame seed oil, rice vinegar, brown sugar, black pepper, garlic powder, onion powder, and minced garlic.
4: Add the crushed beef bouillon cube (if using) and oyster sauce. Gradually add water and whisk until smooth. Set the sauce aside.
5: Cook the udon stir-fry noodles according to package instructions. Drain and set aside.
6: Add the broccoli to the boiling water and cook until it’s bright green and crisp-tender for about 1–2 minutes.
7: Heat 3 tablespoons of oil in a wok or large skillet. Remove the beef from the marinade and stir-fry until browned, about 3-4 minutes.
8: Add broccoli and stir-fry until tender, about 3-4 minutes. Add the sliced green onions and red chilies; stir-fry for 1 minute.
9: Add the cooked noodles to the wok or skillet. Pour the prepared sauce over the noodles and stir-fry everything together.
10: Cook for an additional 2 minutes, ensuring the sauce coats the noodles. Garnish with sesame seeds.
