Butter a 10 diameter cake form with removable sides. Pour the mixture into it. Put it to bake until ready at 356°F (180 °C).
Leave it to cool and cut it into pieces.
Make a sugar syrup by putting the water and sugar in a casserole, heat them and put them to boil, add the juice and rind of half a lemon, stir and let it boil until you get a syrup.
Pour this syrup over the sponge cake.
Leave it for at least 6 hours to absorb the syrup. It's best to eat it the next day.