Let’s get baking! Follow these steps to bring your Apple Cinnamon Crumble Cake to life:

1. Preheat your oven to 350°F (175°C) and grease a 9×13 inch baking pan.
2. In a large bowl, cream together the butter and granulated sugar until light and fluffy, about 3-4 minutes.
3. Add the eggs one at a time, beating well after each addition, then mix in the vanilla extract.
4. In a separate bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg.
5. Gradually add the dry ingredients to the butter mixture, alternating with the sour cream, and mix until just combined.
6. Gently fold in the sliced apples and walnuts (if using) into the batter.
7. Pour the batter into the prepared pan and smooth the top with a spatula.
8. In a small bowl, mix together the brown sugar and remaining flour for the crumble topping with your fingers until it resembles coarse crumbs.
9. Sprinkle the crumble mixture evenly over the batter.
10. Bake in the preheated oven for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
11. Allow the cake to cool in the pan for at least 15 minutes before slicing.

As you bake, let the sweet scent of cinnamon and apples transport you to a place of comfort and warmth.