Prep the aromatics
Trim and cut the frying Scallions into thirds if they are not already cut. Thinly slice the remaining fresh scallions, mince the Garlic, and mince the optional Shallot. Keep the fried-scallion pieces separate from the sliced scallions so they are ready for different jobs later.
Boil the noodles
Bring a large pot of water to a boil and season it well with Salt. Add the Momofuku Soy & Scallion Noodles and cook according to the package directions, but stop 30 seconds before they are fully done so they finish perfectly in the sauce. Before draining, scoop out some Pasta Water and set it aside. Drain the noodles, then rinse them briefly under cold water to stop the cooking and keep them from clumping.
Heat the oil
Set a large skillet or wide sauté pan over medium heat and pour in the Neutral Oil. Let it warm for about 1 minute, until the oil looks loose and shimmery but is not smoking.
Fry the scallions
Add the scallion pieces to the warm oil and cook them gently over medium heat, stirring occasionally, until they are fragrant, lightly browned, and a little crisp at the edges, 10 to 15 minutes. Lift the scallions out with tongs or a slotted spoon and set them aside, leaving the scallion-infused oil in the pan.
Build the sauce base
In a heatproof bowl or directly in the pan if it is safe and roomy enough, combine the sliced scallions, Chili Flakes, Sesame Seeds, minced garlic, Brown Sugar, the minced shallot if using, Soy Sauce, Dark Soy Sauce, and Black Vinegar. Stir everything together so the sugar is evenly distributed before you add the hot oil.
Sizzle the aromatics
Reheat the scallion oil over medium heat until it is very hot and shimmering, about 1 to 2 minutes. Carefully pour the hot oil over the sauce base; it should sizzle right away. Stir well so the aromatics bloom and the sugar starts dissolving into the soy-vinegar mixture.
Toss and loosen
Add the drained noodles to the sauce and toss thoroughly until every strand is coated. If the noodles look tight or dry, add a few tablespoons of the reserved pasta water at a time and keep tossing over low heat until the sauce turns glossy and clings to the noodles instead of pooling underneath.
Finish and serve
Taste the noodles and adjust the balance if needed, then divide them between bowls. Top with the fried scallions and a spoonful of Momofuku Chili Crunch. Serve right away while the noodles are hot and glossy.
