Preheat oven to 350°. Spray a 9- or 10-inch round cake pan or 10-inch round pie plate, or 9-inch square pan with nonstick cooking spray.
Peel, core, and slice apples into bite sized pieces.
Melt butter in a large skillet over medium heat. Add apples, sugar, and cinnamon. Cook for about 3-4 minutes, until the apple just starts to turn opaque, but is still white. Remove from heat to cool.
Whisk flower, baking powder, salt, and cinnamon together in a medium bowl. Set aside.
Stir ¼ cup melted butter with granulated sugar and egg in a large bowl. Stir in milk. Stir dry ingredients into wet and stir until just combined. Pour into prepared pan.
Sprinkled cooled apples evenly over the top of the cake batter.
Make the crumb topping: stir together brown sugar, flour, cinnamon, and melted butter. Sprinkle over apples.
Bake for 30-35 minutes until a toothpick comes out clean.
Store covered in the refrigerator for up to 4 days or freeze for up to a month.