Preheat the oven to 180C/350F/Gas Mark 4 and prepare your baking tin by greasing it generously and lining the bottom with some baking paper.
Put the flour into the large bowl, add baking powder and cinnamon and give it all a mix with a whisk. Alternatively, feel free to sieve your dry ingredients into the bowl.
Add softened butter.
Rub butter into the flour with your fingers (you could use mixer or food processor if you wanted to) until the mix resembles wet sand.
Add sugar and give it all a light mix. Set aside.
Peel, core and thinly slice your apples and place them in a large bowl. Squeeze the juice of half lemon over them to prevent them from getting brown. Set aside.
Add your lightly beaten eggs into the flour/sugar and mix them in gently.
Start adding milk and mixing it in slowly bit by bit until it's all gone and you have thick, batter like mixture.
Add most of your sliced apple to the cake batter, saving some slices to put on top. Mix them in only just and pour in the mixture into prepared cake tin.
Smooth the surface of the cake mixture with spatula and arrange your remaining apple slices on top in any fashion you want.
Sprinkle demerara sugar on top and bake in preheated oven for 50-55 min until nice and golden brown and the skewer inserted into centre of the cake comes out clean.
Important! Once you take your cake out of the oven, let it cool in the tin for good 20 minutes before you take it out onto the rack to cool completely.
Serve dusted with icing sugar or slightly warm with cream or ice cream. Enjoy!