1 cup good mayonnaise
1 cup chopped scallions, white and green parts ( 6 to 7 scallions)
1 cup chopped fresh basil leaves
1/4 cup freshly squeezed lemon juice (2 lemons)
2 teaspoons chopped garlic (2 cloves)
2 teaspoons anchovy paste (optional)
1 teaspoon kosher salt
1 cup sour cream
3 heads Bibb lettuce
2 to 3 tomatoes
Place the mayonnaise, scallions, basil, lemon juice, garlic, anchovy paste, salt, and pepper in a blender and blend until smooth. Add the sour cream and process just until blended. (If not using immediately, refrigerate the dressing until ready to serve.)
Cut each head of lettuce into quarters, remove some of the cores, and arrange on 6 salad plates. Cut the tomatoes into wedges and add to lthe plates. Pour on the dressing and serve