Preheat your oven to 350℉ and grease your 8 inch by 8 inch baking dish. Then start by adding the vinegar to the milk for the batter and let sit while you continue making the other parts of this recipe.

Make the cinnamon filling by stirring together all of the ingredients for the cinnamon filling; brown sugar, flour, and cinnamon.

Then make crumble topping by stirring together the flour, sugar, and cinnamon for the topping. Once stirred, cut in the cold butter until most of the dry ingredients have mixed with the butter.

Finally, make the batter by whisking together the dry ingredients, the flour, cornstarch, baking powder, baking soda, and cinnamon, in a large bowl.

Then in another bowl, whisk together the wet ingredients, the vegetable oil, sugar, vanilla, sour cream, and vinegar & milk mixture. Then pour into the bowl with the mixed dry ingredients and combine well with a spoon.

Pour the rest of the batter on top, and then sprinkle the crumble topping on top of the batter, evenly.

Bake for about 55-60 minutes, or until a toothpick comes out clean. Let cool slightly before slicing, serving, and enjoying!