Ina's Green Goddess Dressing

As a dip, serves 16-24 people

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)
2 teaspoons kosher salt or to taste
1 teaspoon freshly ground black pepper
1 cup sour cream

Directions
Place the mayonnaise, scallions, basil, lemon juice, garlic, anchovy paste (optional), 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.)