In the work bowl of a food processor, pulse together basil, spinach, walnuts, cheese, garlic, vinegar, sugar, salt, and pepper until combined. With processor running, add olive oil in a slow, steady stream until combined. (Add additional oil to reach desired consistency, if needed.)
Transfer pesto to a glass container with a lid. Before closing lid, cover surface of pesto with a thin layer of olive oil. Refrigerate before using, up to a day.
Recipe by TeaTime Magazine at https://teatimemagazine.com/turkey-pesto-sandwiches-recipe/