Preheat the oven to 180°C/350°F/gas 4. Lightly grease a 28cm loose-bottomed tart tin.
Bash 2 tablespoons of demerara sugar in a pestle and mortar until fine, then mix with the remaining demerara so you have a range of textures. Tip into the tart tin and shake around to coat. Tap gently, then tip any excess back into the mortar for later.
Slice the edges off the panettone in strips and use them to line the base and sides of the tart tin, pressing down hard to compact and create a pastry-like shell.
Halve the vanilla pod lengthways and scrape out the seeds, then put both the seeds and pod into a pan on a medium heat along with the cream, milk and butter, and simmer for 5 minutes or until the butter has melted.
Meanwhile, in a large bowl, whisk the eggs and golden caster sugar for 2 minutes, or until smooth. Whisking constantly, add the hot cream mixture to the bowl until combined, then discard the vanilla pod.
Now it’s time to build this crazy comfort pudding. Pour one-third of the custard into the base of the tart and leave to soak in for a couple of minutes.
Tear up all the remaining panettone into rough chunks, soak them in the bowl of creamy custard for a minute or two (the more it sucks up, the better!), then layer up in the shell you’ve created, snapping up and adding little chunks of chocolate and dollops of marmalade between the layers – there’s no need to be neat about it, you want a range of heights, saturation and textures.
Pour over any leftover custard, leaving it to soak in if necessary, then sprinkle with the remaining demerara sugar.
Bake for around 25 minutes, or until set. Allow the pudding to rest for 10 minutes, then serve with cream, custard or ice cream, if you like – it’s delicious cold, too, if you’ve got any leftovers!
If you're pushed for time, assemble the tart the night before, store in the fridge, then bake the next day. Simple!