200ml/7fl oz double cream, whipped until stiff peaks form when the whisk is removed, to serve
For the lime curd, heat all of the lime curd ingredients in a heavy-based saucepan over a low heat for 10-12 minutes, stirring constantly, until the mixture thickens. Strain through a fine sieve and set aside to cool. Once cool, pour into sterilised jam jars.
For the pudding, heat the milk and cream in a separate saucepan until just boiling, then remove the pan from the heat. In a separate bowl, whisk the eggs, salt and sugar together until well combined, then pour the milk and cream mixture over the egg and sugar mixture, whisking until smooth and well combined.
Butter the bread slices and, using about 12 tablespoons of the lime curd, spread curd over both sides of each slice of bread.
Cover the bottom of a greased ovenproof dish with a layer of the bread slices, overlapping the edges of the bread slightly. Sprinkle over some of the fresh and dried cranberries and 1-2 tablespoons of rum, if using. Repeat the layering process once more, or until all of the bread, cranberries and rum have been used up. (NB: You should have enough for two layers.)
Pour the cream and egg mixture over the bread and set aside to soak for one hour.
Preheat the oven to 180C/365F/Gas 4.
Place the pudding dish into a roasting tray. Carefully add enough boiling water to the tray to reach one third of the way up the sides of the pudding dish (this is called a bain-marie). Transfer to the oven and bake for 40-45 minutes, uncovered, or until the custard has set and the top of the pudding is pale golden-brown. (NB: Check the pudding occasionally during cooking, pushing any cranberries that float to the surface back under the custard as it sets, using a fork, to prevent the cranberries from burning.)
Remove the pudding from the oven and from the bain-marie and set aside to cool for 8-10 minutes.
Meanwhile, heat the redcurrant jelly in a saucepan with two tablespoons of water, until the jelly has melted and the mixture forms a smooth sauce. Brush the top of the pudding all over with this mixture, then set aside to cool for a further 10 minutes.