Peel and finely dice the onion. Finely dice the celery. Fill the kettle and boil it.
Heat 2 tsp olive oil in a deep frying pan or wok. Add the onion and celery. Season. Cover. Fry for 5-8 mins till the veg are glossy and soft. Stir now and then.
Fill a heatproof jug with 400ml hot water from the kettle. Crumble in the vegetable stock cube. Stir. Add 100ml of the stock to the onion and celery. Gently simmer for 10 mins till the stock has evaporated.
While the veg cook, scrub and trim the beetroot. Quarter them, there’s no need to peel them. Put the beetroot in a food processor and blitz briefly to make ‘rice’. You may need to do this in two batches if the processor looks too full.
Peel and finely chop the garlic. When the stock has evaporated from the onion and celery, stir in the garlic. Add 1 tsp of the cumin and cook for 1 min. Stir every now and then.
Add the beetroot rice to the pan. Pour in the remaining stock. Gently simmer, without the lid on, for 20-25 mins till the beetroot is soft but still has some bite. Most of the stock should evaporate.
Taste the risotto. Adjust the seasoning if you think it needs it. Spoon the risotto into warmed bowls. Top with a handful of rocket and 2 tbsp ricotta each. Serve immediately.