Combine flour, sugar, baking soda, cinnamon and salt in a large bowl; set aside. Mix together egg and apples; add to flour mixture. Stir in walnuts. Spread in a lightly greased 8"x8" baking pan. Bake at 350 degrees for 25 to 30 minutes, until a toothpick inserted near center comes out clean. Serve warm, drizzled with Caramel Sauce.
Caramel Sauce --- last 6 ingredients
Combine brown sugar, flour and salt in a small saucepan. Gradually add water; stir until smooth. Cook and stir over medium heat until mixture comes to a boil. Cook for one to 2 minutes, until thickened. Remove from heat; stir in butter and vanilla.