Heat butter in a large frypan over medium-high heat. Without crowding, lightly brown scallops in batches. Remove scallops to a casserole dish.
Stir onion and mushrooms into the frypan and cook until the onion is soft and begins to brown. Stir in garlic, tomatoes, wine, tomato pasta sauce, salt, tarragon, rosemary and white pepper. Bring to a boil; cover, reduce heat to low and simmer 15 minutes. Uncover and cook until thick, about 3 minutes. Mix in shrimp and vinegar.
Preheat oven to 200 degrees C.
Spoon sauce evenly over scallops.
Bake in a preheated oven until sauce bubbles and begins to brown at the edges, about 10 minutes. Sprinkle parsley over tops, and serve.