Preheat the oven to 170 degrees C
In a 12-inch cake pan, melt 300g of butter over very low heat, and add the brown sugar evenly over the pan.
Arrange pineapple slices to cover the bottom of the pan.
Beat the eggs whites until double the size, then add granulated sugar gradually, beating well after each addition until medium-size peaks form.
Remove from the mixture and add lemon and the orange zest.
Sift together flour, baking powder, and salt.
Fold in the dry ingredients with some juice and cooking oil.
Spread batter evenly over pineapple in the cake pan.
Bake for 30-40 minutes or until surface springs back when gently pressed with fingertip and a toothpick inserted in the centre comes out clean.
Loosen the edges of the cake with a table knife, let it cool for 5 minutes before flipping onto a serving plate.