01 - Preheat oven to 350°F and lightly grease a 9x13-inch baking pan.
02 - Simmer 1 cup apple cider in a saucepan over medium heat until reduced to 1/2 cup. Allow to cool before use.
03 - In a bowl, whisk together flour, baking powder, baking soda, salt, cinnamon, and nutmeg until evenly combined.
04 - In a large mixing bowl, beat softened butter, granulated sugar, and packed brown sugar until light and fluffy. Add eggs one at a time, mixing well after each addition. Incorporate vanilla extract.
05 - Blend in reduced apple cider and sour cream, mixing until just incorporated.
06 - Gradually mix dry ingredients into wet mixture until no dry spots remain. Avoid overmixing.
07 - Transfer batter to prepared pan, spreading evenly. Bake for 35 to 40 minutes or until a toothpick inserted in the center comes out clean.
08 - While cake is baking, melt sugar in a medium saucepan over medium heat, stirring constantly until deep amber. Add butter, stirring until fully melted. Slowly pour in heavy cream, stir smooth, and add salt. Remove from heat and cool slightly.
09 - Allow cake to cool for 10 minutes. Using the handle of a wooden spoon, poke holes evenly across the cake surface.
10 - Pour about three-quarters of the caramel sauce evenly over the cake, allowing it to seep into the holes. Let cake cool completely.
11 - Whip heavy cream with powdered sugar and vanilla extract until stiff peaks form. Smooth whipped cream over cooled cake.
12 - Drizzle reserved caramel sauce over whipped topping. Sprinkle with cinnamon if desired. Serve chilled or at room temperature.