Place the apples, plums, blackberries, caster sugar and red wine in a pan over medium-low heat. Cook, stirring occasionally, for 15 minutes until the apples are soft. Stir in the creme de cassis or blackcurrant cordial, if using, then allow to cool.
Line the base and sides of a 1.5-litre pudding basin with the bread, leaving enough overhanging the sides to cover the top. Fill with the fruit mixture, packing down well, then cover the top with the overhanging bread, trimming to fit. Cover with plastic wrap. Cut a piece of cardboard to fit, then place on top. Weigh pudding down with cans, then transfer to the refrigerator and chill for at least 4 hours or overnight.
Place mixed berries, icing sugar and lemon juice in a food processor and whiz until smooth. Pass through a sieve, discarding solids. Pour into a jar and chill until ready to serve.
When ready to serve, run a palette knife around the side of the pudding to loosen. Invert the pudding onto a large plate, then brush with some of the berry sauce. Pour the thickened cream over the pudding, then slice and serve with the remaining berry sauce.