Heat the butter in a large saucepan and add the red onion. Cook gently, stirring often, until the onion is soft and translucent.
Add the sliced chestnut mushrooms, garlic and thyme and cook until the mushrooms are soft and most of the excess liquid has evaporated.
Add the risotto rice and stir well then add the white wine and cook, stirring often, until it has all been absorbed.
Pour in a ladleful of the stock and stir until is has been mostly absorbed. Continue to gradually add the stock, a couple of ladleful's at a time and stir the risotto constantly until it has all been absorbed and the rice is tender.
Remove the pan from the heat and stir in the vegan cream, truffle oil, nutritional yeast and plenty of salt and pepper.
To make the garlic mushrooms, heat the vegan butter in a frying pan, add the sliced shiitake or wild mushrooms and the crushed garlic and cook, stirring often, until the mushrooms are soft.
Serve the risotto topped with the garlic mushrooms and a scattering of fresh parsley.