Heat your oven to 220°C/Fan 200°C/Gas 7. Set a large roasting dish on the top shelf to heat up.
Trim and peel your beetroot and carrot. Cut into 2-3cm chunks. Tumble into the warmed roasting dish. Drizzle over 1 tbsp oil and season well. Roast for 25 mins.
Meanwhile, halve, peel and thinly slice your onion. Thinly slice your celery. Add them to the beetroot and carrot. Roast for a further 10 mins or till everything is tender and a little coloured around the edges.
Halve, stone and thinly slice the plums. Pile into a little jar with one of the star anise. Cut a few thin slices from your chilli and add to the jar. Pour in enough balsamic vinegar to cover. Swirl everything together. Set aside to steep.
Blend the hot roasted veg with 500ml-1ltr boiling water and a good pinch of salt and pepper, trickling the water in slowly as you blend, till it’s the right consistency for you. Let the motor run for 1-2 mins to get a really smooth consistency. Blitz in a few slices of chilli and the remaining star anise, ground to a powder, if you have a pestle and mortar.
Simmer the soup with the remaining star anise for 5 mins or grind the star anise and swirl in a pinch or two to taste. Serve the soup topped with a little pinch of the pickled plums and drizzle of balsamic juices.