Begin by slicing the white parts of the scallops into rounds and putting the corals on one side for later.
Then poach the sliced scallops and the grapes in the wine and vermouth – gently and for only one minute. After that strain everything and reserve the liquid.
Next melt the butter in a saucepan then stir in the flour till smooth. Now add the scallop liquid a little at a time, stirring the whole time till you have a smooth sauce. Season with salt and pepper and continue to cook very gently for another five minutes or so. Pre-heat the grill at this point, at its highest setting, for ten minutes. Take the pan off the heat then add the whites and the corals, along with the cream. Give it a stir then bring back to heat, being careful not to let it boil. Divide the mixture between the scallop shells or gratin dishes, then pop them under the grill (four inches from the source of the heat)for 2-3 minutes till browned and bubbling. to brown a little.
Serve garnished with watercress and some good bread to mop up the juices. Note: if you want to make this in advance, that’s fine. In which case, to serve them, once you have the grill really hot, position them six inches from the heat and grill them for about five minutes until as above.