Preheat the oven to 200C/400F/Gas 4.
Heat the butter in a large pan over a medium heat. Add the plums and fry for a few minutes.
Add the split vanilla pod, star anise, nutmeg and cinnamon sticks to the pan. Add the water, red wine, golden syrup and sugar and bring to the boil. Reduce the heat and simmer for 6-8 minutes, until the plums break down to a thick sauce.
Transfer the plum mixture to a deep ovenproof dish.
For the crumble topping, mix the flour and sugar together in a bowl. Rub in the butter with your fingers until the mixture resembles breadcrumbs.
Sprinkle the crumble over the plums and bake in the oven for 20-25 minutes, until golden-brown.
Remove and allow to cool slightly before serving with ice-cream or double cream.