Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.
In a large bowl, whisk together the all-purpose flour, baking powder, and salt.
Cut the cold unsalted butter into the flour mixture using a pastry cutter or your fingers until the mixture resembles coarse crumbs.
In a separate bowl, whisk together the whole milk, eggs, granulated sugar, and vanilla extract until well combined.
Pour the wet ingredients into the flour and butter mixture. Stir gently until just combined to form a biscuit-like batter.
Spread half of the batter evenly into the prepared cake pan.
Arrange half of the thinly sliced apples over the batter in an even layer.
Sprinkle half of the ground cinnamon and half of the light brown sugar evenly over the apples.
Spread the remaining batter over the apple layer, smoothing the top gently with a spatula.
Arrange the remaining apple slices on top of the batter.
Sprinkle the remaining ground cinnamon and light brown sugar evenly over the top layer of apples.
Bake in the preheated oven for 40 to 45 minutes, or until a toothpick inserted into the center of the cake comes out clean and the top is golden brown.
Remove the cake from the oven and allow it to cool in the pan for 15 minutes before transferring to a wire rack to cool completely.
Serve warm or at room temperature, optionally with a pat of butter or a scoop of vanilla ice cream.