Preheat the oven to 180C.
Line the bottom of a square cake pan with parchment paper.
Mix the sliced apples with cinnamon and keep aside.
Sift the flour, baking powder, cinnamon and salt together. Keep aside.
In a large bowl, using the electric mixer, cream the butter and sugar together. Continue till light and fluffy, about 3-4 minutes. Add the eggs one by one and beat till well mixed.
Add the apple puree and vanilla. Beat for another minute or so.
Fold in half the flour mixture. When combined, fold the rest in.
Spread batter in prepared pan and spread the sliced cinnamon-coated apples on top.
Bake for 25 to 30 minutes, or until a cake tester inserted into the middle comes out clean.
Let it cool completely before slicing or serving.
Serve warm with a scoop of ice cream or a dollop of whipped cream; a cup of tea or a glass of wine is optional but highly recommended!