In a small bowl, combine the flour, baking powder, baking soda, salt, and spices.
To the cooled brown butter, whisk in the brown sugar, then the egg and vanilla.
Add in half of the dry ingredients, and mix until just combined.
Whisk in the applesauce and buttermilk.
Then, mix in the rest of the dry ingredients until just combined.
Pour the cooled spiced caramel apples into the cake batter and mix with a rubber spatula until evenly dispersed.
Pour the batter back into the cast iron skillet and smooth out the top.
Sprinkle with turbinado sugar and bake for about 35 minutes or until a toothpick inserted comes out clean.
Allow to cool for about 20 minutes, then drizzle more caramel sauce on top.
Enjoy warm with a big scoop of vanilla ice cream!