Butter the bread and arrange four slices, buttered side down ,in a single layer in the dish. Sprinkle the bread with nutmeg and half sultanas. Arrange another layer of bread, buttered side down, over the fruit, and sprinkle the remaining nutmeg and sultanas on top. Cover with the remaining bread, again buttered side down.
In a bowl, whisk eggs, add cream , milk , vanilla , sugar . Pour the mixture over the bread through a fine sieve. Sprinkle the granulated sugar over the top and let it stand, covered loosely at room temperature for at least one hour, or chill overnight.
Place in a bain-marie … the water should go halfway up the sides of the baking dish and bake in the middle of the oven ( 180c /350f/ gas 4) for about one hour until the top is crisp and golden. Serve warm with whipped cream.