Remove the stalks and wash the currants. Stew gently in the water until tender, and then sieve them. Mix the cornflour to a smooth paste with a tablespoonful of the blackcurrant purée. Put the rest of the purée on to boil with the sugar. When boiling, add the blended cornflour and the lemon juice, and cook for two minutes, stirring all the time to prevent the mixture sticking. Leave to cool. Separate the eggs, beat the yolks, and add to the cooled blackcurrant mixture, mixing well. Whip the egg whites to a stiff foam and fold into the mixture when cold. Pour into a serving bowl. Serve with cream.