Mix the ricotta cheese with the icing sugar. Whip the cream until it forms soft swirls then fold into the ricotta. Reserve a few pieces of the chopped chocolate, apricots, cherries and candied peel and fold the rest into the ricotta mixture.
Line an 18 cm (7 inch) deep round cake tin with 2 pieces of clingfilm so that the base and sides are covered. Arrange half the trifle sponges over the base of the cake tin, trimming to fit. Moisten with half the rum.
Spoon two-thirds of the ricotta mixture over the sponges and spread the surface level. Cover with the remaining trifle sponges and moisten with the remaining rum. Spread the rest of the ricotta mixture on top and sprinkle with the reserved chocolate and fruits, dust with cocoa powder. Chill for 4 hours or overnight.
Loosen the edges and lift the cake out of the tin using the clingfilm. Peel off the film and transfer to a serving plate. Cut into thin wedges to serve. Store in the refrigerator for up to 2 days.