Preheat to oven to 170ºc and line a 33 cm x 22 cm cake pan with non-stick baking paper. 

In a large mixing bowl cream the butter and the sugar together, using an electric whisk until the mixture is pale and fluffy and has increased in volume. Add in the eggs one at a time. Mix well after each addition. Gently mix in the milk and the maple syrup.

Sift the flour, baking powder and cinnamon into the butter and egg mixture. Switch to a spatula or a wooden spoon to mix the flour into the egg mixture being very careful not to over mix.

Spoon the cake batter into a lined baking tray and layer the thinly sliced apples on top.

Sprinkle the demerara sugar over the apples and bake in a preheated oven for about 35 minutes until the cake is golden on top and the cake springs back when lightly pressed. A toothpick should come out of the cake with a few crumbs on the sides.

Let the cake cool in the tin for 15 minutes before turning it out to cool on a rack.