Fennel and Red Grape Salad with Creamy Tarragon Dressing

Name: Fennel and Red Grape Salad with Creamy Tarragon Dressing
Ingredients: 1 tablespoon sour cream; 1 tablespoon mayonnaise; 1 tablespoon lemon juice plus 1/2 teaspoon grated zest from 1 lemon; 5 tablespoons olive oil; 1/4 teaspoon sugar; 1 tablespoon chopped fresh tarragon leaves; 1 tablespoon chopped fresh parsley leaves; 3 romaine hearts , torn into bite-sized pieces (about 12 cups); 3/4 cup red grapes , halved or quartered, depending on their size; 3/4 cup thinly sliced fennel (see related Tip); 1/2 cup spiced pecans (see note above)