Peel the onion, then blitz in a food processor until fine.
Tip into a large casserole pan on a low heat with 1 tablespoon of olive oil and half the butter, stirring occasionally.
Cut cute 1cm florets off the cauliflower, toss with ½ a tablespoon of oil, spread across a baking tray and roast for 20 minutes, stripping in the thyme leaves for the last 5 minutes.
Chuck all the cauli offcuts, stalk and any nice leaves into the processor and blitz until fine.
Bring the stock to a gentle simmer over a low heat.
Stir the rice and blitzed cauliflower into the onion pan, now on a medium heat, to toast for 2 minutes.
Add a ladleful of stock and wait until it’s been fully absorbed before adding another, stirring constantly and adding ladlefuls of stock until the rice is cooked – it will need 16 to 18 minutes.
Add an extra ladleful of stock to make it oozy, finely grate in the Parmesan, then beat in the rest of the butter, season to perfection and turn the heat off.
Cover and leave to relax for 2 minutes.
Serve each portion sprinkled with roasted cauliflower and thyme leaves, draped with prosciutto, and with a drizzle of extra virgin olive oil, adding extra Parmesan, if you like.
