Chop the prawns and scallops. In a heated saucepan, melt the butter and some olive oil, add onions, chopped prawns, scallops, parsley and sauté until prawns turn pink and scallops turn white. Add the ketchup and mustard, flame with brandy. Add fish stock. Add some water to the corn flour and thicken the sauce with it. Finally add a touch of cream. Divine mixture into Four scallop shells , top with some cheese and place under a griddle until cheese turns to a nice golden brown. Top with breadcrumbs, white sauce and grated cheese. Bake until shells turn red-orange. Occasionally check if meat is moist and tender