In a large mixing bowl, whisk together the flour, baking powder, salt, and cinnamon. Set aside.
In a separate mixing bowl, beat the butter and sugar with an electric mixer for 3 to 4 minutes or until light and fluffy. Add the eggs one at a time, mixing well after each one, then mix in the pure vanilla extract. Stop and scrape down the sides of the bowl if needed and mix again.
Add the dry ingredients on low speed in three additions alternating with the milk, beginning and ending with the dry ingredients. Mix in each addition until just combined, making sure not to over mix the batter.
Pour the batter into the cake pan on top of the sliced apples.
Bake for 35 to 40 minutes or until a wooden toothpick inserted into the center of the cake comes out clean.
Remove from the oven and allow to cool for about 10 minutes in the pan, then flip the cake out of the pan and onto a cooling rack to cool completely.