Peel the marrow and discard seeds. Put into a saucepan with enough water to just cover the bottom of the pan and cook until quite soft. Weigh the pulp and to each lb. of pulp add the grated zest and juice of 2 lemons, 1lb. sugar, 4oz. butter and 2 eggs. Put all these together in the top of a double saucepan or basin over hot water and cook gently until thick and smooth. Pour into hot sterilized jars and cover tightly.