Preheat oven to 350℉. Butter and flour a 9" square baking pan. (You can try lining the pan with parchment paper for easier flipping and less mess. Let me know how it goes if you give it a shot!)
Peel, core, and slice apples into ¼ inch thick slices, avoiding slicing too thin to maintain distinct slices rather than applesauce.
Juice half a lemon and toss the sliced apples in a bowl with the lemon juice. Set aside. (Option to add 1/4 tsp. cinnamon to the apples if you want a stronger cinnamon presence in the cake)
In a large bowl, combine flour, baking soda, ginger, ½ teaspoon cinnamon, cloves, walnuts, and salt, stirring until well mixed.
In a medium-sized bowl, mix together applesauce, brown sugar, and cooking oil. Combine the wet ingredients with the dry ingredients and stir thoroughly.
Prepare the filling by combining brown sugar, cinnamon, and cocoa powder in a medium bowl.
Arrange the apples decoratively on the bottom of the pan, covering the entire surface. Feel free to get creative with your pattern!
Gently spread half of the batter into the pan, smoothing it out as best as you can while being careful not to disturb the apples. This should amount to approximately one to one and a half cups of batter.
Evenly sprinkle the cinnamon, cocoa, and sugar filling over the top to cover the surface.
Spread the remaining half of the batter over the filling, smoothing it out carefully to avoid disturbing the filling too much. It's okay if some of the filling is showing; that will become very crunchy. Connect the dollops across the top and smooth them out. If the batter is too thick, you can add a teaspoon of oil to thin it out.
Top with a sprinkling of Muscovado dark brown sugar, cinnamon, and Turbinado sugar for added crunchiness and flavor. (Feel free to experiment with adding more Muscovado sugar throughout the recipe.)
Bake for 35-40 minutes or until a toothpick comes out clean.
Invert the cake onto a parchment-lined baking sheet so that the apples are now on top. Replace any loose apple slices. Sprinkle another tablespoon of brown sugar and a quarter teaspoon of cinnamon over the top of the cake, then place it under the broiler for 1-2 minutes, or until the brown sugar melts onto the apples.
Serve with coffee for breakfast. For a dessert, this cake pairs beautifully with dessert wines.
