Whisk together the cream, milk, sugar, salt, and black walnut extract. Pour the mixture into your ice cream maker and freeze according to the manufacturer's directions.
When the ice cream has almost finished churning, add the chopped walnuts. Allow the machine to mix them throughout the ice cream. Transfer the ice cream to a freezer-safe container and freeze until firm.
Notes
If black walnuts are unavailable, regular walnuts may be substituted. The black walnut extract will add significant black walnut flavor to the ice cream base. My preference is black walnuts, but the ice cream is still delicious without them.