Preheat the oven to 350?F (177?C) and grease a 9?13-inch baking pan or line with parchment paper.

In a medium bowl, mix the brown sugar, granulated sugar, cinnamon, and salt together. Stir in the melted butter. Lightly mix in the flour until crumbles form.

Whisk the flour, baking soda, baking powder, and salt together. Set aside.

In a mixer, beat the butter and granulated sugar together on high speed until smooth and creamy, about 2 minutes.

Add the eggs, sour cream, and vanilla. Beat on medium-high speed until combined, even if it looks curdled.

With the mixer on low, mix in the dry ingredients until smooth, ensuring not to overmix.

Toss the chopped apples with cinnamon.

Spread the batter in the prepared baking pan, top with cinnamon apples, and press in the crumb topping.

Bake for 45-55 minutes, until a toothpick comes out clean. If browning too quickly, loosely cover with aluminum foil.

Let the cake cool for at least 30-45 minutes before slicing and serving.

Top with icing if desired and store leftovers in the refrigerator for up to 5 days.