Salsa di Noci (Walnut Sauce)

Close kin to the familiar basil pesto, salsa di noci also comes from the Italian Riviera and was originally always made in a mortar. Other versions of it include butter, ricotta, Parmigiano, bread crumbs, or smaller proportions of green herb than are called for here. Sometimes there’s no cream; sometimes there’s no garlic. Occasionally, I’ve used walnut…