Place a large saucepan of water over a high heat and bring it to the boil before salting, and leave while you cook the mushrooms.
Heat 1 tablespoon each of the oil and butter in a frying pan over a medium high heat. Add half of the mushrooms and cook, stirring often, until all of the liquid is released has been evaporated and the mushrooms start to caramelise. Remove from the pan and set aside while you cook the remaining mushrooms.
When the second batch of mushrooms are almost done add the first batch to the pan along with the thyme leaves, garlic and balsamic vinegar and cook, stirring, for a minute or two.
Add the wine and cook until most of the liquid has evaporated before adding the cream or creme fraiche. Season with salt and pepper and serve sprinkled with fresh parsley.
For the mushrooms I used a mixture of button mushrooms and portobello. Hugh suggests using chestnut, open-cap and field mushrooms. For the thyme I used approximately 1 heaped tbs of freshly picked thyme leaves.