Grease and line two 8" or 9" cake pans with parchment paper and set aside.
In a large bowl, whisk together the flour, baking soda, salt, pumpkin spice and cinnamon. Set aside.
In a medium bowl, combine the oil, brown sugar, molasses, applesauce, eggs and vanilla.
Make a well in the center of the dry ingredients and pour in the oil-sugar mixture. Whisk to combine until all ingredients are moistened and no dry patches remain.
Grate your apple directly into the bowl and then stir to distribute evenly.
Split the batter amongst the two pans - about 2 1/2 cups of batter per pan.
Bake for 18-22 minutes.
Remove the cakes from the oven and let cool for one minute before turning out onto a cooling rack.
While the cake is cooling, make the cream cheese frosting.
Beat the butter and cream cheese together, then add 2 cups of powdered sugar and the vanilla extract. Adjust to taste and preferred consistency.
When the cakes are cool, place one on your cake stand and place 1/2 cup of frosting ontop. Smooth to cover the whole top with your offset spatula, then sandwich the second layer overtop.
Smooth all but 1/2 cup of frosting all over the cake.
Sprinkle a bit of cinnamon over the top of the cake, if desired.
Add 1/2 cup to 1 cup of powdered sugar to the remaining frosting to make it stiffer, then scoop into a piping bag fitted with a star tip.
Make quick "dabs" of frosting along the edge of the cake by gently squeezing the piping bag and pulling it away firmly after about 1-2 seconds. Do this all around the top edge of the cake, and then just pipe a simple line of frosting along the bottom edge.
Serve with a drizzle of caramel sundae sauce, as desired.