Wash and peel the pears, cut them into 4-6 slices and then into small cubes. Sauté them in a non-stick frying pan, with the thyme and a knob of butter, over a low heat. When they have softened, add the sugar and let them caramelise slightly, then pour in the Vin Santo. Continue to simmer over a low heat, stirring constantly until all the liquid evaporates. Remove the pan from the heat and set aside. Now finely chop the onion and sauté it in a non-stick frying pan with 2 knobs of butter, then add the uncooked rice. Toast the rice over a low heat; to prevent the onion from burning, stir constantly and add a little more butter if necessary. When the rice is a nice golden colour and sufficiently toasted, add the pieces of pear, the cloves and enough hot vegetable broth to cover the rice. Lastly add the saffron, dissolved in 2 or 3 spoonfuls of broth. Cook over a lively heat (adding a little broth if you see that the liquid is absorbed too quickly) until the rice is ready to eat. A tip from La Vialla: the rice is cooked when, if you shake the pan, it comes away from the sides. At this point, turn off the heat, add the cubes of pecorino and a sprinkling or Parmigiano, stir well and serve.