Peel and cut the potato into 2 cm dice. Cook gently in salted water until tender.
Drain the potatoes and allow the steam to evaporate for a few minutes so as the potatoes are dry.
Use a vegetable mill to puree the potatoes. Beat in 50g of butter, the egg yolks and season with nutmeg, Maldon sea salt and pepper. Mix until smooth.
Allow to cool and then transfer the potato mix to a piping bag fitted with a star shaped nozzle.
Prepare the scallops by removing from the shell and separating the orange roe.
Pull away the skirt and discard.
Wash the scallop and the roe under cold water and then dry on paper towel.
Wash the shells, remove any stray pieces of scallop and dry the shells completely.
Pipe a circle of the Duchesse potato around the outside of the shell and allow to cool and set.
Heat the fish stock in a saucepan with the white wine until just simmering. Add the scallops and roes and poach gently for 2 minutes. Remove the scallops form the poaching liquid and then reduce the stock by half. Keep this poaching liquid for the sauce.
Peel and finely dice the shallot.
Melt the butter in a saucepan over a medium heat and sweat the shallot until soft. Add the flour and make a roux.
Whisk in the poaching liquor a ladleful at a time and cook until the sauce thickens.
Add half of the double cream and season with Maldon sea salt and pepper. Continue cooking for a few minutes until the sauce thickens enough to coat the back of a spoon. Add a touch more cream if needed. Allow the sauce to cool.
Melt a knob of butter in a frying pan, add the breadcrumbs and toss to coat them in the butter. Allow to cool and then add the grated Gruyere.
Slice the button mushrooms thinly and juice the lemon.
Cook the mushrooms in the butter with the lemon juice and white wine.
Cook for 5 minutes on a low heat until most of the liquid has evaporated.
Season with a pinch of Maldon sea salt.
Preheat the oven to 200'C.
Put the scallop in the middle of the potato circle.
Top with the button mushrooms, spoon over enough sauce to half cover the scallop and finish with a generous sprinkling of breadcrumbs on top.
Bake in the oven for 15 minutes or until golden on top and the sauce is bubbling.
«Use fresh diver caught scallops for this dish, pasteurised ones have too much water content.»