Heat your oven to 180°C (160°C fan).
Grease your baking tin well with butter.
Line it with baking paper carefully.
This prevents the cake from sticking.
Put butter and sugar in your bowl.
Beat them until light and fluffy.
This takes about 3 minutes.
Add eggs one at a time.
Mix well after each egg addition.
The mixture should look smooth and creamy.
Sift flour and baking powder together.
Fold them gently into the egg mixture.
Add the milk and mix lightly.
Don't overmix or cake becomes heavy.
The batter should be soft and smooth.
Peel your apples with a sharp knife.
Cut them into thin slices carefully.
Remove the cores and seeds completely.
Mix apple slices with ground cinnamon.
This adds wonderful flavor to your cake.
Pour half the batter into your tin.
Spread it evenly across the bottom.
Arrange half the apple slices on top.
Add remaining batter and smooth it out.
Place rest of apples on the surface.
Sprinkle demerara sugar over everything generously.
Put tin in your preheated oven.
Bake for 45-50 minutes until golden.
Test with a skewer in the center.
It should come out clean when done.
The top should be nicely browned.
Remove cake from oven carefully.
Let it cool in tin first.
This takes about 10 minutes.
Then transfer to a cooling rack.
Cut into squares when completely cool.