Sprinkle sugar over the baking paper in the prepared tin, place the slices of apple on top.
Place the butter, jelly and sugar in a bowl, mix thoroughly using the whisk attachment on a mixer. Add the eggs one at a time and continue to beat until the mixture becomes lighter in colour. Combine the polenta, flour, baking powder and salt, mix in. Spread the cake mixture over the apple slices.
Approx. 50 mins. in the centre of an oven preheated to 180°C. Remove from the oven, allow to cool slightly, remove the tin frame, tip out onto a cooling rack and leave to cool completely. Cut the cake in half crosswise, combine the lemon juice and sugar, drizzle over the cut surfaces of the cake.
Mix the mascarpone and jelly, spread over the base, cover with the top half of the cake.
Combine the jelly and water, use to glaze the surface of the cake.