It is quite simply one of the most brilliant hot puddings ever invented. It's so simple but so good – and even better prepared two days in advance.
Lightly butter a shallow oven-proof dish (7 x 9 inches). Remove the crusts from the bread, and cut each slice into 4 triangles.
Melt the butter, chocolate and sugar, with the whipping cream, rum, and cinnamon in a bowl set over a saucepan of barely simmering water. Remove the bowl from the heat and stir well.
In a separate bowl, whisk the eggs and then pour the chocolate mixture over them and whisk again very thoroughly to blend them together.
Spoon a 1cm layer of the chocolate mixture into the base of the dish and then arrange half the bread triangles in overlapping rows. Pour over half the remaining chocolate mixture, then the rest of the triangles, finishing off with a layer of chocolate. Use a fork to press the bread gently down so that it gets evenly covered.
Cover the dish with clingfilm and allow to stand at room temperature for 2 hours before transferring it to the fridge for a minimum of 24 (but preferably 48) hours before cooking.
Bake in the oven at fan 180°C for 30-35 minutes, by which time the top will be crunchy and the inside soft and squidgy. Leave it to stand for 10 minutes before serving.