Combine sliced onions and olive oil in a pan over medium high heat. Cook for 2 minutes, stirring often, then lower heat to medium and cook onions for 10 minutes until they are soft and starting to brown.
While onions cook, bring a pot of salted water to a boil, then cook noodles for 1 minute. Quickly drain, saving 1 cup of the cooking water.
When onions are softened, increase heat to medium high. When the pan heats up, add tomato paste, Soy & Scallion sauce packets (not the dried scallions), and Momofuku Chili Crunch. Stir constantly for 1 minute, until the mixture is combined and tomato paste darkens.
Add 1 cup of pasta water to the tomato paste mixture and 1 cup of milk, stirring until smooth. Bring to a boil, then add the cooked noodles and cook for about a minute, or until the sauce is thick and the noodles are fully coated. Serve with parmesan cheese and fresh basil, if desired.
