Although there's a cider cocktail called the Stonewall, I implore you not to call this unnamed cocktail the Stone Walnut:
3/4 oz nocino (walnut liqueur)
1 oz rye whiskey
Pour into a mug and top with hot unpasteurized apple cider.
This has been our favorite cocktail of cider season. You really, really need to use farmstand apple cider - I don't think anything in a supermarket will come close. Depending on the apples the cider was made with, and how tart it is, you might want a squeeze of lemon juice.
You might also need to adjust the amount of nocino for sweetness - I'm using homemade stuff (which is dead simple if you can get green walnuts - chop them into halves or quarters, cover them in vodka for a couple months, add sugar to desired sweetness).