Put the custard into a pan with the
chocolate pieces. Gently heat, stirring,
until the chocolate has melted into the
custard. Cover with cling film and cool.
Arrange the brownies in the base of
a trifle bowl. Drain the jars of cherries,
reserving the liquid, and scatter over the
brownies. Drizzle over 100ml reserved
liquid. Spoon the cooled chocolate custard
over and chill while you make the topping.
Lightly whip the cream with the crème
fraîche and icing sugar until soft peaks
form. Chill until ready to serve, then pile
on top of the trifle and decorate with grated
chocolate and fresh cherries, if you like.