Spread the panettone cubes into a shallow, buttered 9- or 10-inch square baking dish and sprinkle with the raisins. In a large bowl, whisk together the eggs, milk, sugar, orange zest (if using) and vanilla. Pour over the bread and let stand for an hour, or cover and refrigerate overnight.
When you’re ready to bake, preheat the oven to 350?F. Bake the bread pudding for 45 minutes, until puffed and golden and a knife inserted in the centre comes out clean.
To make the marmalade sauce, warm the marmalade, orange juice and cinnamon in a small saucepan until the marmalade melts and the mixture simmers. Serve warm with the pudding. Serves 8-10.