- Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
- In a medium bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and nutmeg. Set aside.
- In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy. Beat in the eggs, one at a time, then stir in the vanilla extract.
- Gradually add the dry ingredients to the wet ingredients, alternating with the applesauce, beginning and ending with the dry ingredients. Mix until just combined.
- Spread the cake batter evenly into the prepared cake pan.
- In a skillet, melt the 2 tablespoons of butter over medium heat. Add the sliced apples, brown sugar, cinnamon, nutmeg, and lemon juice. Cook, stirring occasionally, until the apples are tender, about 5-7 minutes.
- Stir in the cornstarch-water mixture and cook for an additional 1-2 minutes, until the mixture has thickened. Remove from heat and let cool slightly.
- Spread the apple pie filling over the cake batter in the cake pan.
- In a small bowl, combine the flour, granulated sugar, brown sugar, and cinnamon for the streusel topping. Stir in the melted butter until the mixture resembles coarse crumbs.
- Sprinkle the streusel topping evenly over the apple pie filling.
- Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center of the cake comes out clean.
- Allow the cake to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.
- Serve slices of the apple pie cake warm or at room temperature, optionally with a scoop of vanilla ice cream or a dollop of whipped cream.
Enjoy your delicious Apple Pie Cake!