Preheat the oven to 180ºC/350ºF/gas 4. With a knife, cut the cores out of the tomatoes, then place cut side down in a snug-fitting baking dish with the whole garlic bulb, and scatter over the thyme sprigs. Drizzle with 1 tablespoon of oil, season with sea salt, and roast for 1 hour, or until starting to burst open (the juices will add game-changing flavour later on).
Bring the stock to a simmer. Peel and finely chop the onion and fennel, reserving any herby tops, then place in a large, high-sided pan on a medium heat with 1 tablespoon of oil and 1 knob of butter. Cook for 10 minutes, or until softened but not coloured, stirring occasionally, then stir in the rice to toast for 2 minutes. Pour in the vermouth and stir until absorbed. 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. Beat in the remaining knob of butter, finely grate and beat in the Parmesan, then season to perfection and turn the heat off. Cover the pan and leave to relax for 2 minutes so the risotto becomes creamy and oozy.
Divide the risotto between warm plates, place a tomato in the centre with a little sweet garlic and the herby fennel tops, then drizzle over the tasty tomato juices.
Squeezing the smooth, mild garlic out of its skin after roasting adds a delicious bonus flavour to the risotto.
To make vegetarian: swap Parmesan for vegetarian hard cheese.