Thinly slice the Red Apple (2). Chop the Walnut (1/4 cup).
Preheat the oven to 350 degrees F (180 degrees C). In a large bowl, combine Granulated Sugar (1/2 cup), All-Purpose Flour (2 cup), Baking Powder (1 teaspoon) and Salt (1 teaspoon).
Using a pastry blender, blend the Unsalted Butter (2 ounce) until only small pieces remain. Add Milk (1 cup) and Egg (1). Mix until combined.
Spread half of this mixture into a seasoned cast iron skillet or your choice of greased pan. Place apples in a bowl and mix with Granulated Sugar (1 teaspoon) and a third of the Cinnamon (3 teaspoon).
Arrange apples on top of batter and spread remaining batter carefully over the top.
Combine remaining Unsalted Butter (1/2 cup), Brown Sugar (1/2 cup), Ground Cinnamon (3 teaspoon), walnuts, and remaining All-Purpose Flour (1/4 cup) with a pastry blender or fork until crumbly. Sprinkle over top of cake.
Bake for 35-45 minutes. Let cool and enjoy.