Preheat oven to 350 degrees. Grease and flour one 9x13 inch baking pan.
Sift flour and baking powder together and set aside. Cream butter with the 1 cup of sugar until fluffy. Add eggs and the teaspoon vanilla extract; beat well. Add the flour mixture to the butter mixture 2 tablespoons at a time; mix until well blended. Stir in the grated apple. Pour batter into prepared pan.
Bake 30 minutes. Pierce cake several times with a fork & allow to cool.
Meanwhile, make the apple filling. Melt butter & cinnamon over medium heat. Stir in apples, brown sugar & 3 tablespoons water. Cover & cook stirring occasionally for 5-7 minutes or until very slightly softened. In a small dish combine cornstarch and water. Add to pan while stirring and continue to cook until apples are soft (not mushy) and filling is thickened. Let bubble 1 minute. Cool.
Combine the whole milk, condensed milk, and evaporated milk together. Pour over the top of the cooled cake. Spread the cooled apple filling over top of the cake once the milk has absorbed.
Beat whipping cream, sugar, and vanilla together until thick. Spread over the top of cake. Be sure and keep cake refrigerated. Drizzle caramel topping over top. ENJOY!