Toss raisins into a little bowl and drizzle with rum. Set aside to plump up, at least 30 mins.
Butter a rectangular baking dish and set aside.
Butter each slice of bread on both sides and arrange in the baking dish, overlapping and snug.
Whisk eggs, cream, cinnamon, nutmeg and vanilla.
Pour the custard over the bread and sprinkle the rum-soaked raisins.
Cover with foil and pop into the fridge at least for 30 mins or overnight.
Preheat the oven to 375*F.
Place the baking dish into a deep roasting pan.
Add enough hot water to come halfway up the sides of the dish.
Bake 45 minutes until golden brown.
Carefully remove from the oven.
Lift the baking dish out of the water bath and set onto a metal rack to cool a bit.
Expect a layer of molten butter on top. The pudding will soak the butter up as it cools.
Make the sauce.
Melt the butter over medium heat.
Whisk in the sugar and cream.
Once the sauce begins to boil, reduce the heat and simmer, uncovered for 10 mins, stirring frequently.
Spoon sauce over the warm pudding, sprinkle coarse salt evenly and serve with berries and freshly brewed hot coffee