Melt the butter and fry the onions until golden. Add the mushrooms, stir for 2 minutes, then the green pepper and stir for 1 minute. Add the tomatoes and stir for 3–4 minutes. Add the water and salt and cook for about 20 minutes until the mushrooms are very tender and there is a lot of juice.
While the vegetables are cooking, melt the butter for the sauce in another pan. Remove from the