1. Preheat the oven to 180C.
2. Place the butter in a mixing bowl,grate the garlic straight into the mixing bowl using a Microplane. Add the parsley,lemon zest and a pinch of salt and pepper. Stir the butter well to incorporate the ingredients.
3. Peel the mushrooms and trim the stalk with a paring knife. Smear the garlic butter equally over all the mushroom gills and place two sprigs of thyme on each mushroom. Season each mushroom with a good pinch of salt and pepper.
4. To cook the mushrooms, take four x 30-centimetre squares of aluminium foil. Place a mushroom in the centre of each piece a foil. Bring two opposite corners of foil up over the mushroom,fold and squeeze the foil to seal. Now bring the other two corners up over the mushroom,fold and crunch together to form a tight seal.
5. Place the mushroom parcels on a baking tray,place in the oven and bake for 15 to 20 minutes.
6. When ready to serve,open the packets and carefully lift out the mushroom. Spoon over any of the cooking juice left in the parcel.
If you like this recipe,try Andrew'spine mushrooms in barigoule sauce.