Add the sliced apples to the skillet, followed by the vanilla extract, spices, and chopped walnuts. Cook, allowing the mixture to bubble and the apples to soften slightly about 5 minutes. Pour the bourbon and allow the mixture to bubble once more. Carefully, using a long lighter, ignite the mixture (be sure to have a lid handy to extinguish the fire should it get out of hand). Allow the fire to burn out.