100 g (3 1/2 oz) butter at room temperature, cut into cubes
100 g (3 1/2 oz) demerara sugar
100 g (3 1/2 oz) milk chocolate, very roughly chopped
1 tablespoon custard powder
2 tablespoons cocoa powder
1 tablespoon caster sugar
300 ml (1/2 pint) milk
Roughly chop the pears and place in a bowl, add the muscovado sugar and toss well to coat. Transfer to a large gratin dish.
Place the flour and butter in a food processor and pulse until coarse breadcrumbs form. Transfer to a bowl and stir in the demerara sugar and chocolate.
Scatter the crumble mixture over the top of the pears and place in a preheated oven, 220°C (425°F), Gas Mark 7, for 10–12 minutes until just beginning to brown.
Meanwhile, place the custard powder, cocoa and caster sugar in a heatproof bowl and blend to a paste with about 1 tablespoon of the milk. Heat the remaining milk in a saucepan until almost boiling, then pour on to the custard powder mixture, stirring constantly. Return the mixture to the pan and bring to the boil over a gentle heat, stirring constantly, until thickened.