Process parsley and garlic in workbowl of food processor fitted with steel blade, stopping as necessary to scrape down sides of bowl with rubber spatula, until garlic and parsley are chopped fine (20 one-second pulses); transfer to medium bowl. Whisk in remaining ingredients until thoroughly blended. Spoon about 2 tablespoons over each steak and serve. (Sauce tastes best when used fresh but can be refrigerated, with plastic wrap pressed directly on surface, up to 3 days.)

Makes 1 generous cup