Press the jam through a sieve into a small saucepan and add the water. Heat gently until softened, then spread in a thin layer over the tops of the cooled cakes.
Arrange 15–16 of the cakes in a staggered circle on a round flat platter or tray, at least 35 cm (14 inches) in diameter. Using a small, fine sieve or tea strainer, dust the cakes on the platter with plenty of icing sugar.
Fold a piece of paper into 4 thicknesses, then cut out a holly leaf shape, about 6 cm (2½ inches) long. Press a holly leaf paper template gently on to the centre of 4 more cakes and dust lavishly with icing sugar. Carefully lift off the templates by sliding a knife under the paper to remove them without disturbing the sugar. Repeat on the remaining cakes. Arrange the cakes in a circle on top of the first layer.
Cut the grapes into small clusters. Tuck all the fruits into the gaps around the cakes and into the centre of the plate. Finish by arranging small sprigs of bay leaves around the fruits.