Step 1

Cut scallions crosswise into thirds, separating dark green parts from white and pale green parts. Slice lengthwise into very thin strips, keeping dark green and white parts separate.

Step 2

Pour oil into a cold large wok or high-sided skillet. Add white parts of scallions to oil and set over medium-low. Cook until oil starts to bubble, about 5 minutes. Add dark green parts of scallions and stir to combine. Cook, stirring occasionally, until scallions are crisped and deep golden brown, 20–30 minutes. Do not rush this; slow, gradual browning as the liquid in the scallions evaporates will yield the best flavor.

Step 3

Using a spider or slotted spoon, transfer scallions to paper towels to drain. Let scallions and oil cool. Pour oil through a fine-mesh sieve into an airtight container; discard solids. Cover and chill scallion oil until ready to use.

Step 4

Cook noodles in a large pot of boiling water according to manufacturer’s directions, adding 1 Tbsp. reserved scallion oil to the cooking water when you add the noodles. Drain noodles, reserving ½ cup cooking liquid, and return to pot. Add ½ cup scallion oil and toss to coat. Add soy paste and toss to combine. Add soy sauce and toss again, adding cooking liquid as needed to loosen sauce.

Step 5

Transfer noodles to a bowl or platter and top with three-fourths of crispy scallions. Serve with remaining scallions in a small bowl alongside.

Step 6

Do Ahead: Scallions can be fried 1 day ahead. Keep scallion oil chilled; store scallions between layers of paper towels in an airtight container at room temperature.