Preheat the oven at 200°C.
Prepare a 20 cm square baking tin by lining with parchment paper or foil. Lightly butter this and keep aside.
In a bowl, using an electric whisk, beat the eggs, sugar and vanilla for around 5 minutes until thick and mousse like.
In a small saucepan, melt the butter on a low heat. Add the milk. Whisk well and then pour into the egg mixture beating on low speed as you pour.
Sift the flour, cinnamon and baking powder into a large bowl.
Fold the dry ingredients into the egg mixture until there are no lumps. Pour half of this batter into the prepared pan.
Layer with half of the sliced apples. Pour over the remaining batter and layer with remaining apples. Sprinkle 1 tbsp granulated sugar evenly over the top and a touch of cinnamon powder.
Bake this in preheated oven at 200°C for 10 minutes. Reduce temperature to 180 and bake for another 20 minutes until a tester comes out clean. Cool for 10 minutes, peel off lining paper and cut into 16 or 20 pieces.
Serve warm, with some whipped cream on the side if you like.