For the cake:
For the apple caramel layer:
1. Preheat oven to 350F (175C). Grease a 9-inch (23cm) springform pan.
2. In a large bowl cream butter and sugar, add eggs, one at the time and beat until combined. add milk, vanilla extract and beat until combined. add flour, baking powder, salt, cinnamon and stir until incorporated. set aside.
3. Make the caramel: In a small bowl stir melted butter and brown sugar. Transfer to the prepared pan.
4. Peel the apples and thinly slice. Arrange the apples over the caramel in a circular pattern with each one overlapping the other. Repeat until the entire bottom of the pan is covered.
5. Pour cake batter on top of apples and smooth the top of the batter
6. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Remove from the oven, allow to cool for 3-5 minutes, turn out onto serving platter. Let cool slightly before serving.