Preheat oven to 400°F. Grease and flour one nine-inch cake pan.
In a medium bowl, mix together the flour, baking soda, baking powder, salt, and cinnamon. In a larger bowl cream together the butter and sugar with an electric mixer until light and fluffy. Add the vanilla and egg and beat well to combine.
With the electric mixer on low, add the flour mixture in three additions, alternating with the buttermilk and ending with the flour mixture. Fold in 1 cup of the chopped apples. Spoon the batter into the cake pan and smooth. Sprinkle with the rest of the chopped apples, the nuts, and the cinnamon sugar.
Bake for about 20 to 25 minutes or until a toothpick inserted into the center of the cake comes out clean. Let it cool for about 10 minutes before removing it from the pan.