2. Heat the butter in a frying pan and add the mushrooms, garlic and thyme. Cook for a few minutes until the mushrooms are soft, darkening and release their juices. Stir in the soy sauce.
4. Score a ½ inch border around each edge (taking care not to cut right through). This will allow the outer area to puff up more and frame the mushrooms.
5. Pile mushrooms into the centre of each tart. Don't go too close to the edge, and stay away from the scored outer area. But pile them up so you have lots on each piece.