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

Make the crumb topping: Mix brown sugar, granulated sugar, cinnamon, and salt together in a medium bowl. Stir in the melted butter. Using a fork, lightly mix in the flour until crumbles form. Don’t overmix.

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

Using a mixer, beat butter and granulated sugar on high speed until smooth and creamy, about 2 minutes. Scrape down the sides of the bowl as needed. Add eggs, sour cream, and vanilla. Beat on medium-high speed until combined.

With the mixer on low speed, mix in the dry ingredients until smooth. Do not overmix. The batter will be thick.

Toss the chopped apples and cinnamon together.

Spread the batter evenly into prepared baking pan. Top evenly with cinnamon apples. Top with crumb topping, pressing it down so it sticks.

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

Remove from oven and set on a wire rack. Allow to cool for at least 30-45 minutes before slicing and serving.

Top with icing, if desired. Cover leftover cake tightly and store in the refrigerator for up to 5 days.