Preheat the oven to 325°F. Lightly spray a 9×13 inch baking pan with cooking spray and set aside.
In a small bowl, mix together the milk and vinegar. Set aside to “sour”.
In a large bowl, beat together the brown sugar and vegetable oil. Add in the egg until fully incorporated. Mix in the “soured” milk. Add in the baking soda, vanilla and flour, and mix in until fully incorporated.
Fold in the apple. Pour the batter into the prepared pan.
In a small bowl, mix together the white sugar, cinnamon and butter. Sprinkle evenly over the batter.
Bake in the preheated oven for 45 minutes.