Like the mushrooms Mark Peel and I cooked under the spit-roasted leg of lamb, these taste all the more fantastic for cooking under lamb chops, if that is what you are serving them with. But they are also wonderful without the meat juices and, in this version, are purely vegetarian.
Clean the mushrooms with a soft brush or cloth. Put them in a large bowl and toss with the olive oil, thyme, salt, and pepper. Put the mushrooms on a baking sheet and bake for 8 to 10 minutes, or until just tender. Set aside at room temperature for up to 6 hours before serving.