Method

1. For the potatoes, boil them until tender. Drain them, put them back in the pan and dry them for 1-2 minutes over a low heat. Take off the heat and mash the potatoes with the butter, nutmeg, salt and pepper, then beat over a low heat until fluffy. Take the potatoes off the heat and beat in the egg yolks to thicken. Adjust the seasoning. Let the purée cool slightly, then spoon it into a large plastic sandwich bag with a 2cm/3?4in cut in a corner (or piping bag with a plain nozzle) and pipe a generous border of potato around each scallop shell.

2. Discard the white muscle from each scallop and cut any large scallops horizontally in half. Heat the fish stock and wine in a pan, add the scallops, cover and poach 1-2 minutes until the scallops just whiten (remember that they will cook further in the sauce). Transfer them to a bowl, reserving the stock separately.

3. Cook the mushrooms, covered, with the lemon juice, salt and pepper, in a thin film of water until tender, about 5-7 minutes. If any liquid remains, simmer uncovered until it has evaporated. Add the mushrooms to the scallops.

4. For the sauce, boil the reserved stock for 10 minutes until reduced to 450ml/16 fl oz. Fry the shallots in the butter until soft, 1-2 minutes. Stir in the flour and cook until it’s foaming. Whisk in the stock and bring to a boil, whisking, then simmer until the sauce thickens to coat a spoon, 3-5 minutes. Add the crème fraîche and any liquid released by the scallops, and simmer until the sauce reaches coating consistency. Season.

5. Heat the oven to 200C/Gas 6/fan 180C. Stir the scallops and mushrooms into the sauce and spoon into the shells. (Can be prepared ahead to this stage and kept in the fridge for 6-8 hours.) Sprinkle with the breadcrumbs and melted butter. Set the shells on a baking sheet, steadying them on a slice of bread or a bed of foil. Bake until browned and bubbling, 12-15 minutes. Serve very hot.