Brown Sugar Apple Upside Down Cake With Apple Cider Caramel And Spiced Walnuts

["In a large pot, bring the apple cider to a boil. Reduce heat slightly, and simmer the cider until it reduces to about a cup. Do not stir the cider after this point (it may crystallize if over-agitated).", "Continue to reduce the cider until it begins to get thick and caramelize. When the caramel is thick and could coat a spoon, remove the pot from the heat.", "Stir in the butter and salt. Spread half of the caramel at the bottom of a greased 8"" cake pan. Reserve the other half of the caramel.", "Fan the apples into the base of the prepared cake pan (with caramel in the base) into a circle, with the points of the apples going to the center. Set aside.", "Cream the butter and sugar until light and fluffy. Add the eggs one at a time, scraping well after each addition. Add the vanilla, mix to combine.", "Alternately add the milk/heavy cream and the dry ingredients, mixing just to combine.", "Scoop the prepared batter into the pan atop the apples. Bake at 350 until baked through, about 15-25 minutes, or until a tester comes out clean.", "Heat a small saute pan over medium heat. Add the walnuts, and toast, tossing occasionally, until fragrant, about 1 minute.", "Add the cinnamon, nutmeg, and cloves, and continue to cook, tossing to coat. Let cool completely before using them to garnish the finished cake. Serve the cake warm, topped with reserved apple cider caramel and the spiced walnuts."]