To begin, prepare a 9" round pan with non-stick spray. Preheat your oven to 350.
To a small mixing bowl, add your butter and microwave till melted. Add your brown sugar and cinnamon, and stir together till smooth. Spread across the bottom of your baking pan in an even layer.
Arrange your apple slices on top of the topping, going around the pan and lightly overlapping each apple slice (and adding some slices to the middle) till most of the topping is covered.
To a large mixing bowl, add your butter and sugar and beat together with a mixer till creamy. Add your applesauce, vanilla and eggs and mix again briefly.
To the same bowl, add your flour, cinnamon, nutmeg, allspice, baking powder, and salt. Mix together till smooth. While slowly mixing, add your milk till you have a smooth cake batter.
Pour your cake batter across the top of your apple topping and spread into an even layer.
Bake in the oven for 37-40 minutes, or till the cake is springy to touch and a toothpick inserted comes out clean.
Let cool 30 minutes. Gently run a knife around the edge of the cake, separating the edge from the pan. Put a large, flat plate on top of the pan. Flip the pan and plate over, and let the cake release onto the plate. Remove the pan.
Let the cake cool to slightly warm or room temperature. Slice, serve, and devour!
Stored covered on the counter, this lasts 1-2 days. Or, store it in the fridge and it will last about a week.