Wash and dry the apples; use a paring knife to cut a hole at the top, and remove the core and seeds. Place apples at the bottom of the crock pot. Mix the brown sugar, oats, chopped walnuts, cinnamon and butter. Stuff each apple with the filling. Pour the apple cider into the bottom of the crockpot before setting it to low for 4 hours. Serve with ice cream.
