Preheat oven to 180 C and butter a 2 litre baking dish.
Leave bread out to become slightly dry then butter both sides of bread. Arrange one layer of buttered bread on the bottom of the baking dish. Sprinkle with half of the currants (and all of the candied lemon or orange peel if using). Cover with the remainder of bread and currants.
Combine milk, cream, sugar and zest. Add milk mixture to eggs while beating vigorously. Pour milk and egg mixture over bread. Top with a sprinkle of freshly grated nutmeg.
Bake on centre rack in preheated oven for 30 to 40 minutes until crust is a deep golden brown. Serve warm with custard or cream.