Plums cleaned of seeds, cut or leave it and put it into a saucepan for cooking jam. Fill halfway with water, bring to boil, reduce fire to minimum and cook, stirring constantly, about 1.5-2 hours. Add sugar, chopped nuts and cook for another 20-30 minutes. If you like nuts are soft, add them 20 minutes early than sugar. 10 minutes before end of cooking add the butter. Immediately put in jars and roll up. Store in the refrigerator – a little sugar, it's not too good in the heat is stored. This jam goes very well as a filling in pastries.