Put the stock in a small saucepan over a low heat to keep it hot. In a large saucepan, heat the oil, then add the onion and fry for 5 minutes. Stir in half of the grated beetroot, along with the chopped thyme and risotto rice.
Cook over a low to medium heat for a further 2 minutes, then start adding the hot stock, a ladleful at a time, making sure the liquid is absorbed before adding more – this will take about 20-25 minutes. Test a few grains of rice – it should be firm, but cooked through.
Whizz the remaining beetroot until you have a smooth purée, then stir into the risotto with the last ladleful of stock, cooking until the liquid is almost all absorbed and the risotto is a creamy consistency.
Stir in half the goats’ cheese until it melts into the risotto, and then stir in most of the rocket.
Spoon onto plates, scatter with the remaining goats’ cheese and garnish with the thyme sprigs and the remaining rocket leaves.