Preheat oven to 350�F / 180�C. Prepare cake tin with parchment paper. Put pineapple slices at the bottom of the cake tin. Separate eggs and put egg whites in a mixing bowl. Keep yolks for later. Measure flour and mix it with the baking powder in a different bowl. Beat egg whites with electric mixer until hard peaks form. Add egg yolks to it one by one and the vanilla extract whilst beating the egg whites. Mix in the flour too. Pour batter in the cake tin on top of the pineapple slices. Put it in the preheated oven for 45-50 minutes or until toothpick comes out clean. Flip it on a cooling rack to cool down completely before slicing it up.