Preheat oven to 350 degrees F. Spray a 9x13 baking dish with non-stick cooking spray; set aside.
Using your stand mixer with the paddle attachment, cream together butter and brown sugar, until fluffy, about 3 minutes. Add eggs, making sure each egg in incorporated.
In a medium bowl, add flour, baking soda, cinnamon and salt. Whisk together.
With the stand mixer on slow, add to the wet ingredients. Alternate with the sour cream and vanilla. Ending with the flour mixture.
Fold in apples. Pour batter into the prepared baking dish, spreading out to the edges and making it even.
In a small bowl, combine the sugar, flour, cinnamon and cold butter. Mix until it resembles coarse crumbs. You can use a fork, pastry blender or your hands. Hands work best for me.
Make crumbs by taking a handful and squeezing it together. Then carefully break the ball into small crumbs all over the batter.
Bake 35-40 minutes, or until golden brown and cake is set. Let cool on a wire rack or stove for at least 10 minutes before applying the glaze.
To make the glaze, combine the brown sugar, vanilla and water. Mix until smooth. Drizzle over the cake and let it harden slight.
Serve warm and enjoy!