Peel and core the quinces and cut the flesh into small cubes. Put the cubes into two pints of water and bring to the boil. Add the sugar, remove from the heat and stir until the sugar dissolves. Return to the heat and cook gently until the fruit is soft but not broken. Meanwhile put the cores and peel into the remaining water and cook until the pulp is reduced by half. Strain the liquid into the quinces. Boil hard to setting point. Cool a little and stir before putting into warm pots. This gives a clear red jelly with small cubes of quince.