The wine is poured into a saucepan, add the onion and bring to the boil. Reduce heat and boil until there is 1/4 of the liquid. Add the butter, stirring continuously. Season with salt and pepper to taste and set aside. Heat a little butter in a pan, add peeled, cleaned and chopped tomato and green pepper and stew. Tomatoes are added to the sauce, stir and serve.