Preheat oven to 375°F. Grease a 9×13 inch baking pan. In a medium size bowl, mix together the apples, brown sugar, walnuts and cinnamon. Arrange the apple mixture evenly in the bottom of the baking pan.
Beat butter and brown sugar with an electric mixer on medium until light and fluffy. Add in eggs, one at a time and continuing to beat. Then stir in milk, All Bran Buds, caramel extract and sour cream.
In a large bowl, mix together the flour, cinnamon, nutmeg, salt, baking powder. Add wet ingredients to dry ingredients and stir to combine.
Spoon cake batter over the apples in the baking pan. Bake for 30 to 40 minutes or until toothpick comes out of the center clean.
Let cool in the pan for 15 minutes. Then place the cooling wrack on top of the cake and carefully turn it upside down and remove the pan.