For the parmesan crisps, preheat the oven to 180C/350F/Gas 4.
Place a sheet of silicone paper onto a baking sheet. Using a 10cm/4in chefs' ring, pack in some grated parmesan to come 1cm/½in up the inside of the ring. Remove the ring, leaving a disc of parmesan. Repeat to make three crisps.
Bake in the oven for about five minutes, or until melted and golden-brown, about five minutes. Remove from the oven and while still warm, gently curl up the edges of the melted cheese crisp. Allow to cool and set.
For the scallops, preheat the grill to a medium heat.
With a sharp knife, carefully prise open the scallop shells and remove the scallops whole, pulling off the membrane which surrounds it and discarding it. Discard the flat halves of the shells and scrub the other halves to use later.
Heat the oil and butter in a very hot pan and sear the scallops until they are golden-brown on the outside and cooked through, about three minutes per side. Remove from the pan and set aside.
In the same pan, fry the chopped shallot and pancetta until they start to colour. Add the watercress and stir for about a minute, until wilted.
Fill the shell halves with the shallot, pancetta and watercress mixture. Place a cooked scallop on top of each.
Add the balsamic vinegar to the pan used to cook the shallot mixture and bring to a simmer, scraping up the bits from the bottom of the pan. Pour over the scallops in their shells.
Place on a baking tray and grill for 2-3 minutes, until just bubbling.
To serve, arrange the scallops in their shells on a serving plate and tuck a parmesan crisp into each shell.
