Brush a 1.25 litre (2 pint) bombe mould or pudding basin very lightly with oil. Pour the orange juice into a shallow bowl.

Using three-quarters of the trifle sponge cakes, dip one side of each into the orange juice and use to line completely the sides and base of the mould with the darker sugar-coated sides facing inwards.

Place all the Ricotta cheese in a large bowl and stir in the remaining ingredients, mixing well. Spoon into the prepared mould and level the surface. If necessary, trim the ends of the sponge cakes level with the top of the filling.

Dip the remaining sponge cakes in the orange juice and use to cover the top of the cassata. Cover and refrigerate overnight.

Uncover, then carefully run a palette knife down the sides of the sponge lining to loosen. Invert a serving plate on top of the mould. Hold the plate and mould firmly and invert, giving a sharp shake halfway round. Carefully remove the mould from the cassata.

To decorate: whip the cream until standing in stiff peaks, then spoon into a piping bag fitted with a star nozzle. Pipe cream decoratively around base of the cassata, then pipe a ring on top. Arrange the halved orange slices overlapping on top of the ring of cream and serve at once or refrigerate for up to 1 hour before serving.