Heat the oil in a large frying pan over a medium heat, add the chopped onion and cook for 4-5 minutes, or until softened but not browned.
Add the garlic and mushrooms and cook for 3-4 minutes.
Add the rice and stir to coat all the grains with oil. Turn up the heat, add the white wine and simmer for 2-3 minutes.
Reduce the heat and gradually add the stock, a ladleful at a time, until all the liquid has been absorbed.
Stir in the butter and cream and season well with salt and freshly ground black pepper.
To serve, place the risotto into a bowl and sprinkle over the thyme leaves.