Preheat the oven to 190°C/gas 5. You’ll need to wash the beetroots well – they have a habit of attracting grit to the base of their leave stalks. Cut the leaves off 2cm above the top of the beets and set aside. Place the unpeeled beets in a sink of tepid water and leave to sit for 5 minutes, then carefully rub them with your fingers or a gentle brush to dislodge any dirt. Change the water and wash the leaves, then drain and keep separate.
Heat an ovenproof sauté pan that has a tight-fitting lid and sauté the onion in 2 tablespoons of olive oil until just beginning to caramelize. Add the beetroots, rosemary and a teaspoon of salt, and fry for another 2 minutes. Add the vinegar and 4 tablespoons of water, and stir it all together, then seal the pan tightly (or transfer to a roasting dish, which you’ll need to seal tightly) and roast until the beets are cooked through. Beets like the ones in the photograph took 25 minutes; ones the size of walnuts will take up to 45 minutes – just poke them with a skewer, which should just go through when they’re done.
Heat a wide pan and add the remaining oil, then add the garlic and sauté until golden. Add the beetroot leaves and the wine or water, and cook over a moderate heat, stirring constantly, until the leaves have wilted. Season with salt and pepper, or a little chilli powder.
Once the beetroots are cooked, toss them with the leaves and all the juices from both the pan and roasting dish. Scatter the cheese on top and serve.