Spaghetti with Scallion Sauce

Preparation

1. Step 1

   Cook spaghetti in a 6- to 8-quart pot of boiling salted water until al dente.

   Step 2

   While pasta cooks, heat 3 tablespoons olive oil in a 12-inch heavy skillet over moderate heat until hot but not smoking, then cook scallions and garlic, stirring occasionally, until scallions are softened and garlic begins to turn golden, about 5 minutes.

   Step 3

   Transfer scallion mixture to a blender and add zest, salt, pepper, remaining olive oil, and 1/2 cup pasta-cooking water, then purée until smooth. (Use caution when blending hot liquids.)

   Step 4

   Drain pasta in a colander and return to pot.

   Step 5

   Toss pasta with scallion purée, cheese, and salt and pepper to taste over moderate heat until pasta is well coated.