Arrange the pear slices in the bottom of a greased 1.5 litre (2½ pint) ovenproof dish.
Sift the flour, cocoa powder and baking powder together into a large bowl and add the caster sugar, milk, melted butter and egg. Beat with a hand-held electric whisk until smooth and creamy, then pour over the pears.
Combine all the sauce ingredients in a saucepan and heat over a low heat, stirring, until the sugar has dissolved. Bring to the boil, then pour over the pudding.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 35–40 minutes until the sponge is risen. Leave to stand for 3–4 minutes before serving. Serve with custard or vanilla ice cream.