Scrub and de-beard the mussels. Discard any which are broken. If there are any which are open give them a sharp tap on the work surface. If the mollusc is alive it will close of its own accord. Any which remain open are dead and must be discarded. Use a large wide-based shallow saucepan to cook the mussels. Heat the fish stock in the pan until bubbling. Add the mussels in a shallow layer in the pan. Cook them in about 3/4 batches. It is important to cook the molluscs quickly and to remove them from the liquor as soon as the shells open so that they are tender. Overcooking them will toughen them. Using a slotted spoon, remove the opened mussels to a bowl and continue to cook the rest. Remove the meat from the shells and save. Pour the cooking liquor and any liquid in the shells through a fine sieve to remove any grit or bits of shell. This will form the basis of the sauce. Peel and slice the scallions. Peel and finely chop the garlic. Take the leaves from the rosemary stems and chop. Skin, seed and chop the tomato flesh. Pour the mussel liquor into a wide shallow pan and add the cream, chopped garlic and rosemary. Reduce all together to concentrate the flavours and caramelise the cream slightly to give a nutty flavour. Add the scallions and cook in the sauce for a minute or so. Add the tomato flesh and mussels and heat through. Season with lots of freshly ground black pepper, the sugar and a little salt if it is needed. remember that the mussel juices will be salty, so taste first. Serve sprinkled with the freshly chopped chives. DISCLAIMER(c) Copyright 1996 - SelecTV Cable Limited. All rights reserved. Carlton Food Network http://www.cfn.co.uk/