Preheat the oven to 350°F (175°C). Grease a 9-inch round springform pan and line the bottom with parchment paper.
Core the apples and cut them into thin slices. You can leave the peel on for the pretty red edges shown in the photo.
Toss the apple slices gently with the lemon juice, sugar, and cinnamon. Set aside while preparing the batter.
In a medium bowl, whisk together the flour, baking powder, salt, and cinnamon.
In a separate large bowl, beat the softened butter and sugar for about 2–3 minutes, until pale and fluffy.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla.
Add half of the dry ingredients, followed by the milk and sour cream. Add the remaining dry ingredients and mix just until combined.
Spread the batter evenly into the prepared pan.
Arrange the apple slices generously over the top. Slightly overlap them in small fans or circular sections to create the apple-heavy appearance in the photo.
Brush the apples lightly with melted butter.
Bake for 40–50 minutes, until the edges are deep golden brown and a toothpick inserted into the cake portion comes out clean.
Cool in the pan for about 15 minutes before removing the sides of the springform pan.
Once slightly cooled, dust generously with powdered sugar.