1. In a frying pan melt the butter on a medium heat and fry off the pancetta.
2. Chop the leek, if you have a food processor with chopping function this will save time. Add the leek to the pancetta and reduce the heat. Sweat the leek down until the pancetta is well cooked and the leek is well softened. Season well.
3. In a pan, reduce the fish stock until you have syrup about 100ml liquid. Add the vermouth and cream. Reduce, taste and season. Stir into the leek and pancetta pan.
4. Clean the scallops. Take them out of their shells, cut off the roes and discard. Give 4 of the shells a really good clean.
5. On a baking tray make 4 ‘nests’ out of foil (these are to place the scallops on so that they stay upright.)
6. Place the shells on top of the foil nests, evenly spoon the creamed leek and pancetta mixture between the scallop shells and place 2 scallops on top of the mixture in each shell. Refrigerate for 30 minutes.
7. Cut the puff pastry sheet into 4 and indent a scallop shell so you have a lovely shell indentation on the pastry. Place over the shells with the indentation facing up. Shear off the spare pastry with your hands and press lightly to seal. Glaze with egg wash and rest again in fridge for another 30 minutes.
8. Cook in preheated oven 190°C for 15 minutes.