Creating this amazing Salted Caramel Apple Crumble Cake is easy if you follow these simple steps:

1. Preheat the Oven: Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking dish.

2. Prepare the Cake Batter: In a large mixing bowl, combine the flour, sugar, baking powder, baking soda, and salt. Add the softened butter, buttermilk, eggs, and vanilla extract. Mix until well combined and smooth.

3. Fold in Apples: Gently fold the diced apples into the batter until evenly distributed.

4. Prepare the Crumble Topping: In a separate bowl, mix together the oats, flour, brown sugar, and cinnamon. Pour in the melted butter and stir until crumbly.

5. Assemble the Cake: Pour the cake batter into the prepared baking dish, smoothing it out evenly. Sprinkle the crumble topping generously over the batter.

6. Bake: Place in the preheated oven and bake for 40-45 minutes or until a toothpick inserted in the center comes out clean.

7. Make the Salted Caramel Sauce: In a medium saucepan, heat the granulated sugar over medium heat, stirring constantly until it melts and turns a golden amber color. Remove from heat and carefully whisk in the butter. Once melted, gradually add the heavy cream and salt. Stir until smooth and set aside.

8. Cool the Cake: Once the cake is baked, remove it from the oven and allow it to cool in the pan for 15-20 minutes.

9. Drizzle with Caramel: When the cake is slightly cooled, drizzle the salted caramel sauce over the top, allowing it to soak in.

10. Serve: Cut the cake into squares and serve warm or at room temperature.