in a large bowl, beat together the butter and white sugar until fluffy then add in the eggs and vanilla and beat again until combined. Stir in the milk and combine.
Sprinkle the surface of the cake mixture with the all-purpose flour, then sprinkle in the cinnamon, baking powder, and salt. Stir everything together with a spatula just until combined.
Pour the batter over the apples in the pan. The batter is not runny so do your best to spread it evenly to cover all the apples and come to the edges of the pan.
Bake in the oven for 50-60 minutes. (The cake is done when a you can insert a toothpick in the center and it comes out clean)
Let the cake cool for 15 minutes and while it's still warm, run a knife around the edges to make sure it's loosened from the pan.
Place your serving dish or plate on top of the pan and carefully flip the cake over onto the dish. You may need to jiggle the pan slightly to get the cake to fall out. (I would suggest using oven mitts)
Serve warm with whipped cream, or ice cream!