This is Ina Garten’s recipe.  Excellent.

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

2 teaspoons kosher salt

1 teaspoon freshly ground black pepper

1 cup sour cream

Serve with tomatoes and bibb lettuce.