1-First Step: Preparation and mise en place Start by preheating your oven to 350°F (175°C). Prepare a 9×13-inch cake pan by lining it with parchment paper or thoroughly greasing it with butter or cooking spray. Gather all ingredients and ensure your eggs and sour cream are at room temperature this ensures they incorporate smoothly into the batter for even baking. Peel, core, and dice your apples into uniform 1/2-inch pieces for consistent cooking.

2-Second Step: Prepare the apple filling In a large bowl, combine the diced apples with 2 teaspoons of cinnamon and 1/2 packed cup of dark brown sugar. Toss well to ensure the apples are evenly coated with the sugar and spice mixture. Set aside while you prepare the other components. This step allows the apples to macerate slightly, releasing some of their juices and creating a more flavorful filling. If you have time, letting them sit for 10-15 minutes intensifies the flavor even more.

3-Third Step: Make the crumb topping In another large bowl, mix 2 cups of all-purpose flour, 1/2 packed cup of dark brown sugar, 2 teaspoons of cinnamon, and 1/4 teaspoon of fine sea salt. Pour in the 3/4 cup of melted butter and mix by hand using your fingers or a fork. Continue mixing until large, coarse crumbs form. If the mixture seems too wet and sticky, add a little more flour, one tablespoon at a time, until you achieve the desired crumbly texture. Set aside while you prepare the cake batter.

4-Fourth Step: Prepare the dry ingredients In a medium bowl, whisk together 3 cups of all-purpose flour, 1 teaspoon of baking soda, 1/2 teaspoon of baking powder, and 1/2 teaspoon of fine sea salt. Whisking these dry ingredients together ensures that the leavening agents are evenly distributed throughout the flour, which helps the cake rise uniformly. Set this mixture aside.

5-Fifth Step: Mix the wet ingredients In a large bowl, beat 1 cup of vegetable oil and 1 1/4 cups of granulated sugar together until well combined. Add the 3 large eggs one at a time, beating until each egg is fully incorporated before adding the next. Then mix in 1 cup of full-fat sour cream and 2 teaspoons of vanilla extract until the mixture is smooth and creamy. This combination of oil and sour cream is what makes this cake exceptionally moist and tender.

6-Sixth Step: Combine wet and dry ingredients Using a spatula, gently fold the flour mixture into the wet ingredients. Be careful not to overmix stop as soon as you no longer see streaks of dry flour. Overmixing develops gluten, which can make the cake tough instead of tender. The batter will be thick and creamy, perfect for holding the apple filling and crumb topping.

7-Seventh Step: Assemble the cake Spread half of the batter evenly in the prepared pan. Top with the apple filling, spreading it out evenly over the batter. Carefully spoon the remaining batter over the apples, spreading gently to cover completely. Finally, sprinkle the crumb topping evenly over the top of the cake. The layered approach ensures every bite contains delicious apple filling surrounded by tender cake and crispy topping.

8-Final Step: Bake and serve Bake for 50-60 minutes until a toothpick inserted in the center comes out clean, or an instant-read thermometer inserted into the center reaches 200°F (93°C). If the crumb topping begins to brown too quickly, loosely cover the cake with aluminum foil for the last 10-15 minutes of baking. Remove from the oven and cool on a wire rack for at least 30 minutes before serving. For a beautiful finish, dust with powdered sugar or drizzle with a simple glaze just before serving. Enjoy warm or at room temperature with your favorite morning beverage.