To start the stock, put the mussels in a wide, lidded pan (they must not be stacked more than 2 shells deep). Add the whole bottle of wine, cover and bring to the boil over a high heat. Give them a shake and continue cooking fiercely until the mussels open. Pour the lot through a colander into a bowl and leave to drain and cool.
Next, peel and behead the prawns (reserve the tails in the