Start this recipe by placing the diced pears, butter and sugar into a pan and caramelize for 5 minutes or so. Remove off the heat and allow to cool. Meanwhile, heat the milk, water and orange zest in a pan till almost boiling. In a large bowl, lightly whisk together the sugar, corn flour, egg yolks and vanilla essence. Pour the hot milk over this mixture whisking constantly then pour back into the saucepan. Add in the chopped dark chocolate and whisk together until the chocolate melts and the custard boils. Remove off the heat and cool slightly. Spoon half of the cooked pears into 4 glasses and crumble over half of the vanilla sponge. Drizzle with a tot of liqueur. Pour over half of the chocolate custard and allow to cool slightly before repeating the process with the remaining pears, sponge, liqueur and custard. Chill for an hour then serve topped with the crunchy chocolate muesli and dusted with icing sugar.