1. Fill a large bowl with water and add ice cubes. In a stockpot or other tall wide pot, cook the noodles in abundant boiling salted water until al dente, about 3 minutes. Drain the noodles and transfer to the ice water. When cold, drain and transfer to a medium bowl. Drizzle in oil to coat the pasta lightly and set aside.

2. Heat the pot over high heat. Add the oil and swirl to coat the bottom. When the oil is hot, add the scallion whites, the larger quantity of the greens, the ginger and star anise and saut? until softened, about 1 minute. Add the stock, bring to a simmer, and reduce by one quarter, about 5 minutes. Add the soy sauce, sesame oil, carrots, noodles and shrimp. Simmer until the shrimp are just cooked through, about 3 minutes.

3. Transfer to four individual soup bowls, garnish with the remaining scallion greens, and serve.