Preheat oven to 350 degrees. Cut a piece of parchment paper to fit the bottom of a 9-inch round cake pan. Spray pan liberally (bottom and sides) with vegetable spray. Place the parchment in the bottom of the pan and spray the parchment with vegetable spray. Set aside.
Spread ¾ cup walnuts on a sheet pan and toast in the oven for 8-10 minutes or until the nuts are golden and fragrant. Set aside.
In a 2-cup glass measuring cup, add 1 cup buttermilk, ½ cup applesauce, 1 large egg, 2 tablespoons rum and 1 teaspoon vanilla. Whisk to combine. Set aside.
In a large mixing bowl combine 1½ cups all-purpose flour, 1 cup light brown sugar, 1 teaspoon baking soda, ½ teaspoon baking powder, 1 teaspoon cinnamon, ⅛ teaspoon cloves, ½ teaspoon nutmeg, ⅛ teaspoon allspice and ½ teaspoon salt.
Whisk to combine, then add the liquid ingredients and use a rubber spatula to blend until the batter is well mixed and there are no dry bits left.
Add 1 apple, the toasted walnuts and ½ cup golden raisins. Use a rubber spatula to fold them into the batter several times to distribute evenly.
Pour the batter into the prepared pan and bake for 40-45 minutes or until a cake tester comes out clean.
Turn the cake out onto a wire rack and remove the parchment paper from the bottom. Cool to room temperature.
Place a cake plate on top of the cake and invert it. Sprinkle with powdered sugar if desired.
Notes
Make the cake a day ahead and keep it wrapped in cellophane overnight; it gets moister overnight.
The cake will last for 2-3 days wrapped in cellophane at room temperature.
For longer storage, refrigerate and let the cake rest at room temperature for 20 minutes before serving.
This apple cake freezes well. Wrap it in two layers: the first is plastic wrap, then freezer paper or foil.