Combine the lettuce, arugula, radishes, cucumbers and sunflower seeds in a large bowl. Add the dressing, season with salt and pepper, and gently toss.
Combine 1/2 cup each mayonnaise and sour cream, 1/3 cup each chopped parsley and chives, and 1/4 cup chopped tarragon in a blender. Add 2 anchovy fillets, 1 minced garlic clove, 1 tablespoon capers, the juice of 1 lemon, 1/2 teaspoon kosher salt and a few grinds of pepper; puree until smooth.
Courtesy of Food Network Magazine