Gently fry the onion in two tablespoons of the olive oil at medium heat. When it begins to brown, reduce the heat to medium low and continue cooking until golden brown. Add the tomatoes, gently breaking them up with a wooden spoon or fork. Bring the heat back up to medium and simmer gently for about five to seven minutes, until you have a thick, somewhat chunky, sauce. Season with salt and pepper to taste and, if necessary, add one teaspoon sugar to balance acidity. Remove from heat and set aside. You can make the sauce ahead and refrigerate for up to one day.

In a separate skillet, sear the scallops on medium-high heat in two tablespoons olive oil, allowing them to develop a nice brown crust, about one to two minutes per side. Remove the scallops to a plate and deglaze the pan with vermouth, quickly pouring in the tomato sauce afterward. Stir to allow the flavours to blend, and heat until piping hot. While the sauce is cooking, mix one tablespoon of the parsley with the bread-crumbs, and set aside.

Arrange the empty, clean scallop shells or individual heatproof serving vessels on a baking sheet and spoon two tablespoons of the sauce into each. Place a scallop in the centre of the sauce. Sprinkle with the breadcrumb parsley mixture and place in the oven under the broiler until breadcrumbs have browned and sauce is bubbling. Remove from oven, drizzle each serving with a little olive oil, and sprinkle with the remaining fresh parsley. Serve immediately.

Tip: Cleaned scallop shells are sometimes available where you would buy cookware, or ask your fishmonger to keep the shells for you so you can use them for baking. A tablespoon of salt on each serving plate will make a nice bed to steady the scallop shell and prevent it from rocking around.