Preheat oven to 350 degrees F. Grease an 8″ cast iron skillet or 9″ cake pan with nonstick cooking spray. Set aside.
Peel, core, and chop apples. I used a food processor after I cut apples in chunks. This gets them diced up in nice pieces. Set aside. In a medium-sized bowl, whisk together dry ingredients: flour, baking soda, cinnamon, and salt. Set aside.
In a bowl attached to a stand mixer (or with a hand mixer), cream together butter and sugar until light and fluffy. Add in egg and beat until blended. With mixer on low speed, gradually add in dry ingredients, making sure to not overmix. Stir in apples.
Pour batter into prepared skillet/pan, spreading even across. Bake for 25-30 minutes or until the top springs back when touched lightly with your finger.
In a saucepan, melt the butter, brown sugar, and salt. Bring to a boil, stirring with a whisk, then remove from heat and stir in vanilla extract and evaporated milk until smooth.
To serve, spoon 2-3 tablespoons of caramel sauce onto plate, place cake on top, and drizzle with additional caramel sauce. Also great served with whipped cream and/or ice cream. Cake should be served warm or at room temperature.
If you like nuts in your baked goods, you can add a 1/2 cup of chopped pecans.
This cake gets better as it ages, keeps for a week in the fridge, and freezes well.