In a medium-size mixing bowl, combine the dry ingredients. Stir and set aside.
In a large mixing bowl, combine the wet ingredients.
Using an electric mixer, mix until well combined. Set aside.
Chop the walnuts.
Finely chop a Granny Smith Apple.
Prepare the Apple Walnut Cake
Add the dry ingredients to the wet in 2 batches.
Mix well until well combined, however DO NOT OVERMIX.
Add the chopped walnuts and apple to the batter. Fold ingredients into the batter.
Pour batter into a well-greased 9" round cake pan. You can also use a square cake pan.
Bake cake for 40 minutes at 350 degrees. Make sure you check the cake after 30 minutes every 5 minutes as oven temperatures vary. The cake is done. Let it cool for 45 minutes before flipping.
Make the Salted Caramel Frosting
In a large mixing bowl, combine all the ingredients except milk and salt. So combine butter, powdered sugar, vanilla, and store-bought caramel sauce. Blend with an electric mixer.
Add milk and salt. Mix well.
Now you should have perfectly smooth and creamy salted caramel frosting.
Once the cake cools, carefully flip it onto a cake stand. Frost with Salted Caramel Frosting once completely cooled. Drizzle caramel sauce on top and garnish with chopped walnuts.