Preheat the oven to 350°F (175°C). Grease and flour an 8-inch (20cm) round cake pan.
Place the sliced apples in a bowl and toss with lemon juice to prevent browning. Set aside.
In a medium bowl, whisk together the all-purpose flour, baking powder, and salt. Set aside.
In a large bowl, cream the softened butter and granulated sugar together with an electric mixer on medium speed until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Reduce the mixer speed to low and alternately add the flour mixture and milk to the butter mixture, beginning and ending with the flour mixture. Mix until just combined; do not overmix.
Pour half of the batter into the prepared cake pan and spread evenly.
Arrange half of the sliced apples over the batter in a single layer.
Pour the remaining batter over the apples and spread evenly. Top with the remaining apple slices arranged decoratively.
In a small bowl, mix the brown sugar and ground cinnamon together. Sprinkle this mixture evenly over the top of the cake.
Bake in the preheated oven for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and let it cool in the pan for 15 minutes.
Run a knife around the edges of the cake to loosen it, then invert onto a wire rack to cool completely before serving.