Cook noodles for 3 minutes, then drain, saving ½ cup of the noodle water.
While the noodles cook, melt butter in a small pot until it’s sizzling. Add scallions, garlic, and toasted sesame oil and cook for 2–3 minutes, until the scallions are soft and the butter is nutty and golden.
Into the butter mixture, stir 3 tablespoons of noodle water, noodle sauce packet, 1 teaspoon of Momofuku Chili Crunch, and cooked noodles. Return to heat for 30 seconds or so, until the sauce coats the noodles. Add more noodle water, as needed, if the noodles are too dry. Taste and adjust the seasoning with Momofuku Soy Sauce.
Top with sliced scallions and furikake, if desired.
