Preheat the oven to 180°C (350°F). Grease and line an 8-inch (20cm) round cake pan.
Peel, core, and slice apples very thinly, ideally with a mandoline.
The slices shoud be about 2 mm thick.
In a bowl, add eggs with sugar and vanilla.
Mix until light and foamy, for about 5 minutes.
Add melted butter and mix to combine.
Add milk and mix until smooth.
Sift in flour, baking powder, and salt.
Gently fold until combined.
Add apple slices to the batter.
Gently fold until they’re evenly coated.
Pour the mixture into the prepared pan, spreading evenly. Sprinkle a little cinnamon on top.
Top with lightly toasted almond flakes.
Bake for 35–40 minutes, or until the top is golden and a skewer comes out mostly clean (it may still be a little moist inside because of the thin apples).
Let the cake cool in the pan for 10 minutes, then transfer to a wire rack.
Dust with powdered sugar before serving, if desired.