Roasted Red Pepper Sauce

In a skillet, cook onion in 1 tablespoon oil over moderate heat, stirring until softened. Add garlic and cook for 30 seconds more.

Transfer onion mixture to a food processor and add roasted peppers, basil, remaining 2 tablespoons oil, and salt and pepper to taste. Blend sauce until smooth and transfer to a small bowl. (Sauce may be made up to 3 days ahead and chilled, covered.)

To roast red bell peppers

Using a long-handled fork, char peppers over an open flame or on a rack set over an electric burner, turning them until skins are blackened, 4 to 6 minutes. (Or broil peppers on a rack of a broiler about 2 inches from heat, turning them every 5 minutes for 15 to 20 minutes, or until skins are blistered and charred.) Transfer peppers to a paper bag and let stand until cool enough to handle. Keeping peppers whole, peel them, starting at blossom end. Cut off pepper tops and discard seeds and ribs.