Preheat the oven to 400 degrees and place six (1 1/2-cup) gratin dishes on 2 sheet pans.
Melt 4 tablespoons of the butter over medium heat in a medium saucepan. Add the flour and cook for 2 minutes, whisking constantly. Add the seafood stock and whisk until it is smooth and thickened. Whisk in the cream, curry powder, 1 1/2 teaspoons salt, and 1/2 teaspoon pepper. Bring the sauce to a boil, lower the heat, and simmer for 10 minutes, stirring occasionally. Set aside.
Heat the remaining 4 tablespoons of butter in a large (12-inch) sauté pan over medium-low heat. Add the shallots and sauté for 2 to 3 minutes, until tender. Slice the mushroom caps 1/2 inch thick, add to the shallots, and cook for 8 minutes, stirring often. Add the Cognac and cook for 1 to 2 minutes, until most of the liquid has evaporated. Sprinkle with 1 teaspoon salt and 1/2 teaspoon pepper and set aside.
Combine the bread crumbs, parsley, Gruyère, and olive oil in a medium bowl and stir to moisten the crumbs. Set aside.
Add the mushrooms to the cream sauce. Add the scallops and 1 1/2 teaspoons salt, mix well, and divide among the gratin dishes. Sprinkle the bread crumb mixture evenly on top and bake for 20 minutes, until the scallops are cooked and the sauce is lightly browned and bubbly. Serve hot.