Follow the directions of the Spaghetti (450 gram) package for al dente pasta, but subtract 1-2 minutes from what they suggest. We will be cooking this again in a frying pan so we want to under-cook the pasta.
Once the noodles are done, pour in into a strainer and lightly rinse off the extra starch and set aside.
Cut the Onion (1) in half, then and slice them into thin half moon slices and set aside.
Combine the Dark Soy Sauce (1 1/2 tablespoon), Soy Sauce (5 tablespoon), and Granulated Sugar (1 tablespoon) into 1 bowl and set aside.
Cut the Beef (500 gram) thinly against the grain and put it into a bowl.
Marinate the beef with 2-3 teaspoons of the soy sauce mixture from step 2 and Corn Starch (1 teaspoon) for 5-10 minutes.
In a frying pan (preferably a non-stick), add 2-3 tablespoons of oil and set it to high heat and wait for it to get hot.
Add in the onions and cook it for 3 minutes until soft and golden.
Add in the beef and cook for 3-5 minutes until it looks done.
Add in the spaghettini and then add the sauce mixture on top of everything and cook for 2-3 minutes until everything is nice and brown and evenly mixed. Serve and enjoy!