Heat the oil and butter in a frying pan, add the garlic, thyme and mushrooms and fry over a high heat for 3-4 minutes, or until just cooked. Season with salt and freshly ground black pepper and sprinkle over the parsley. Set aside to cool. Brush one side of each sheet of filo pastry all over with a little olive oil. Place one sheet of filo pastry on top of another to create two layers of pastry, then spoon a quarter of the mushroom mixture into the centre of the pastry. Cover with a few slices of Brie cheese, then gather up the corners of the pastry to create a parcel and secure tightly. Brush all over with olive oil and place onto a baking tray. Repeat the process with the remaining filo pastry. Bake the parcels in the oven at 210`c for 10-15 minutes, or until the pastry is cooked and golden brown. Serve whilst still warm with a crispy rucola salad.