1-Preheat oven to 350°F (177°C) and grease or line a 9×13-inch pan with parchment paper for easy removal.

2-Prepare Crumb Topping: In a bowl, mix brown sugar, granulated sugar, cinnamon, and salt. Stir in melted butter until combined, then lightly mix in flour until crumbles form. Chill in the refrigerator or freezer until needed.

3-Prepare Cake Batter: Whisk together 3 cups flour, baking soda, baking powder, and 1 teaspoon salt. Set aside. Beat softened butter and 1 1/2 cups granulated sugar until light and creamy, then add eggs, sour cream, and vanilla; beat until combined. Gradually mix in dry ingredients on low speed just until combined; do not overmix.

4-Toss chopped apples with 1 teaspoon cinnamon to enhance their flavor.

5-Spread batter evenly into the prepared pan, layer apples evenly over the batter, and firmly press the chilled crumb topping over the apples.

6-Bake for 45-55 minutes, or until a toothpick inserted into the center comes out clean. If the topping browns too quickly, cover loosely with foil for the last 10-15 minutes.

7-Cool the cake in the pan for at least 30-45 minutes before slicing, and drizzle with optional icing if desired.