Photograph: Brett Stevens
Put the mushrooms in a lidded casserole dish. Add a few sprigs of thyme and the garlic and pour over the red wine – it should just cover the mushrooms – then add the balsamic vinegar. Bring to the boil, cover and simmer for 30 minutes or until the mushrooms are tender.
When the mushrooms are cooked, remove them with a slotted spoon to a warmed platter and discard the thyme. Turn up the heat and reduce the wine mixture to a quarter of its original volume – this will take about 15 minutes. Season and spoon over the mushrooms and garnish with some fresh thyme.
Get ahead: make up to a day ahead; chill. Reheat on the hob.