Wash the fruit well, then put on the stove in a saucepan without adding any more water. Cover with a lid, and let the fruit get thoroughly heated all through until it comes to a boil, but do not boil it. Stir occasionally. When well heated, mash the fruit well with a wooden potato masher, then strain through a fine sieve, being careful to get every drop of substance from the fruit. Sweeten the juice with sugar to taste, add a few drops of wine or lemon juice, put back on the stove, and cook until it thickens, stirring occasionally. Serve with cake, fritters or puddings. Blackberries, strawberries or raspberries, make a nice sauce.