Put the kelp in a saucepan with 300ml/10fl oz water and bring to the boil. Add the scallop roes, reduce the heat and simmer for an hour.
Pass the stock through a fine sieve into another pan and add the soy sauce. Bring back to the boil and simmer until the volume of the liquid has reduced by half. Set aside.
Fill another pan with water. Add the sea spaghetti and a pinch of salt and cook for 5 minutes, or until tender. Drain and set aside.
Heat 250ml/9fl oz grapeseed oil to a shallow frying pan placed over a medium heat.
Fry the fish scales until crisp and golden brown, drain on kitchen paper, season with salt then set aside.
Preheat a grill or barbecue to hot.
Brush each scallop with the remaining grapeseed oil. Place the shell directly on top of the coals and grill until cooked through and charred. Remove the shells and put the scallops on a board to rest.
To serve, carve each scallop into three thick slices. Put the sea spaghetti into bowls and pour over the broth. Add the scallop slices, drizzle over a little sea truffle oil and top with the fish scales.