In large pot, bring 4 quarts salted water to a boil.
In blender or food processor, combine remaining ingredients and process until smooth. Transfer mixture to top of double boiler or metal bowl set over saucepan of simmering water. Heat sauce, stirring constantly, until mixture is heated through but not boiling. Remove top of double-boiler or bowl from heat.
Add pasta to boiling water, stirring to prevent sticking. Cook until just tender, about 10 minutes. Reserve 1/2 cup pasta cooking water and drain pasta in colander. Return pasta to pot and add sauce and reserved cooking water, tossing gently until well combined. Garnish with chopped chives and serve hot.