Slice onion into large wedges. Peel garlic, crush with the flat side of knife, then roughly chop. Cut carrot into thin julienne.
Bring a pot of water to a boil and lightly salt.
Pat beef slices dry, then toss in a mix of cornstarch and a pinch of salt.
2. Cook beef and start cooking noodles
Heat a couple tablespoons of vegetable oil in frying pan over high heat.
Add beef, shaking off excess starch to the bowl. Stir-fry for about 2 minutes, letting it sear — slices are thin and cook quickly. Transfer to a plate lined with paper towel.
Do not wash frying pan.
Put noodles carefully into boiling water.
For the first minute, stir several times to prevent sticking.
Cook for 6 more minutes over medium heat, then drain and rinse thoroughly under running cold water.
3. Cook vegetables
Add carrot and onion to frying pan.
Stir-fry for 1–3 minutes, depending on how much crunch in your veggies you like. Add all of the garlic and a small pinch of salt.
4. Finish
Return beef to pan, add black pepper sauce and noodles, toss until everything is evenly coated with sauce and heated through.
Note: sauce is quite spicy, peppery — use soy sauce and a splash of noodle cooking water to loosen consistency, but taste for salt as you go.
5. Serve
Finish with a sprinkle of sesame seeds.