Shellfish Stock

Lightly sweat off the vegetables in a little olive oil,
colour until golden brown and add the roasted shells,
tomato purée, star anise, peppercorns and lemon.
Combine everything together. De-glaze the pan with
the white wine, add the water and bring to the boil
gently. Skim off the impurities, then simmer for 1½
to 2 hours, reducing by one-third. Remove from the
heat and allow to settle. Pass through a fine sieve or
chinois and use as required.