You only need:
500ml cream (most recipes call for double cream but we do this with single cream and it is lighter and nicer)
85ml lemon juice (and zest if you wish)
Put the cream and sugar in a pan, stir it a few times and bring it to boil. Lower the heat and let it boil for three minutes while you stir it regularly. Take it off the heat, add the lemon juice (and zest if using it) and let it cool down. Pour it onto glasses or cups and refrigerate it overnight. We serve it with 'cat's tongues' (see recipe)
The children did all the measuring and stirring.