Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
In a medium bowl, stir together the flour, baking soda, baking powder, salt, and cinnamon.
In a large bowl, cream together the butter and sugar until light and fluffy. Beat in the eggs one at a time, then stir in the vanilla. Beat in the flour mixture alternately with the buttermilk, mixing just until incorporated. Fold in the diced apples and walnuts (if desired). Spread evenly into the prepared pan.
Bake for 40 to 45 minutes in the preheated oven, or until a knife inserted into the center of the cake comes out clean. Cool before serving.
Interesting Facts
Apple cake is a very popular dessert in the United States.
The first known recipe for apple cake was published in 1796.
Apple cake is a traditional dessert served during the Jewish holiday of Rosh Hashanah.