For the bread pudding: Preheat oven to 350 degrees F. Grease an large baking/roasting pan.
Combine sugar, cinnamon, and nutmeg in a large bowl. Beat in the eggs until smooth, then work in the heavy cream. Add the vanilla, then the bread cubes. Allow bread to soak up custard.
Place the raisins in the greased pan. Top with the bread-custard mixture, which prevents the raisins from burning. Bake for approximately 25 to 30 minutes, or until the pudding has a golden brown color and is firm to the touch. If a toothpick inserted in the pudding comes out clean, it is done. The mixture of pudding should be nice and moist, not runny or dry.
For the rum sauce: Place the cream in a small saucepan over medium heat, and bring to a boil. Whisk cornstarch and water together, and add to cream while whisking. Bring to a boil. Whisk and let simmer for a few seconds, taking care not to burn the mixture on the bottom. Remove from heat.
Stir in the sugar and rum. Taste to make sure the sauce has a thick consistency, a sufficiently sweet taste, and a good rum flavor.
Serve pudding right out of the oven with the warm rum sauce...you can even top with whipped cream!