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

Make the crumb topping: Mix the 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. Place in the refrigerator or freezer until needed.

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

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter and granulated sugar together on high speed until light and creamy, about 3 minutes. Add the eggs, sour cream, and vanilla. Beat on medium-high speed until combined. Scrape down the sides and bottom of the bowl as needed. 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 the prepared baking pan. Top evenly with cinnamon-coated apples. Top with crumb topping. Press the crumb topping tightly down into the cake.

Bake for 45-55 minutes. The cake is done when a toothpick inserted in the center comes out clean. If the top or edges are browning too quickly, loosely cover with aluminum foil.

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

Drizzle with optional icing, if desired.

Cover leftover cake tightly and store in the refrigerator for 5 days.