Preheat oven to 325 degrees F and grease a 9×13 inch pan with cooking spray.
In a large bowl, whisk together brown sugar, oil, egg and buttermilk.
Then stir in baking soda and vanilla.
Lastly, mix in flour and apples.
Pour batter into prepared pan.
In a small bowl, combine sugar, cinnamon, and butter, mixing gently with a fork.
Spread it evenly over the batter.
Bake for 40-45 minutes or until golden brown.
Serve warm or at room temperature.
