Preheat the oven to 350°. Line a 9x9 baking pan with parchment paper and spray with non-stick spray. Set aside.
In a medium bowl combine butter, granulated sugar, brown sugar, egg and vanilla. Combine with a hand held mixer {stand mixer or by hand} until creamy.
Add flour, salt and baking powder and mix to combine. The mixture might be a bit crumbly but that is alright.
Add the milk all at once and combine until you have a nice cake batter. Pour half of the batter into the prepared 9x9 pan. Top with the chopped apples.
To make the crumb topping, combine the butter, brown sugar, flour and cinnamon in a medium bowl. Cut the butter into the other ingredients until you have crumbs. Do not over mix or you will have a paste. Spread half of the crumbs over the top of the apples.
Add the remaining cake batter on top of the apple and crumbs, spread in an even layer. Top with remaining crumbs.
Bake for 40-45 minutes or until a toothpick inserted near the center of the cake comes out clean. Serve warm or cool on a wire rack. Store leftovers in an airtight container at room temperature or in the refrigerator for up to 4 days. Freeze for up to 3 months.