Preheat the slow cooker if necessary; see the manufacturer's instructions. Butter the inside of 4 metal pudding moulds, each 250 ml (8 fl oz), and base-line each with a circle of greaseproof paper.
Put the measured butter, sugar, flour, egg, cocoa, baking powder and cinnamon in a bowl and beat them together with a wooden spoon until smooth.
Arrange 7 cherries in the base of each pudding mould. Roughly chop the remainder and stir them into the pudding mix. Spoon the mixture into the pudding moulds and level the tops. Loosely cover the tops of the moulds with foil and put them in the slow cooker pot. Pour boiling water into the pot so that it comes halfway up the sides of the moulds, cover with the lid and cook on high for 1½–2 hours or until the puddings are well risen and the tops spring back when pressed with a fingertip. Lift the puddings out of the slow cooker pot.
Make the sauce. Put the chocolate and cream in a small saucepan and heat gently, stirring occasionally, until melted. Loosen the edges of the puddings, turn them out into shallow bowls, peel away the lining paper and pour the sauce around them before serving.