Wash and trim scallions. Bring large pot of water to a boil. Have a large bowl of ice water nearby. When water boils, add salt, when it comes back to the boil, drop in half of the scallions and blanch for 10 seconds. Remove scallions from water with tongs and drop in ice bath. Plunge remaining scallions for 10 minutes and drop into ice water. When scallions are thoroughly chilled, drain them and squeeze dry. Roughly chop the blanched scallions. Place scallions in blender. Add 1/4 cup oil. Puree scallions, stopping frequently to scrape down sides of blender, until coarsely pureed. Add rest of oil and whirl until well blended. Pour mixture through a coarse sieve into a bowl, then pass again through a fine sieve. Use as garnish. Will hold 2 to 3 days.
Make sure to choose very fresh, very green scallions for the best flavor and color.