Preheat oven to 350 degrees F.
Prepare a 9 x 13 inch pan by spraying with cooking spray.
With an electric mixer, combine oil, eggs, vanilla and sugar.
Add flour, baking soda and salt to wet ingredients, and mix until combined.
Stir in apples and walnuts.
Pour into prepared cake pan.
Bake for 45 minutes or until golden brown.
While the cake is hot, prepare caramel sauce by cooking brown sugar, white sugar, water and flour until mixture becomes clear in color.
Add butter and vanilla. Stir until butter is melted.
Pour over hot cake.
Let cool long enough for the sauce to set up.
Cut into pieces and enjoy!