Preheat your oven to 350 degrees F and lightly coat a 9x13 inch baking dish with cooking spray.

In a large mixing bowl, beat the softened butter and brown sugar together until the mixture is smooth and creamy.

Add the vanilla, eggs, and sour cream to the butter mixture, whisking until the batter is well combined.

Stir in the flour, baking powder, baking soda, salt, and cinnamon until just incorporated, then gently fold in the chopped apples.

Spread the batter evenly into your prepared baking dish.

In a separate small bowl, combine the topping flour, brown sugar, and cinnamon, then stir in the melted butter until the mixture looks like coarse crumbs.

Sprinkle the topping evenly over the surface of the cake batter.

Bake for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Allow the cake to cool in the pan for at least 15 minutes before slicing and serving.