Cut romaine and iceberg lettuces into 1-inch pieces.
In a large salad bowl, toss together the romaine and iceberg lettuces, onion rings, sweet pepper, black olives, and feta cheese. Drizzle with the Sherry Wine Vinaigrette. Toss all to coat. Makes 6 servings.
In a screw-top jar, combine olive oil, salad oil, sherry or white wine vinegar, shallot, coarse (kosher) salt, and pepper. Add tarragon and chives. Cover and shake well. Serve immediately or store, covered, in the refrigerator for up to 1 week. Shake before serving. Makes 1-1/3 cups.