1 (750-ml) bottle dry white wine, divided
3 pounds fresh mussels, cleaned
6 tablespoons (¾ stick) unsalted butter
1½ cups chopped yellow onion (2 onions)
1 large leek, white and light green parts, cleaned and chopped
2 carrots, chopped
4 teaspoons minced garlic (4 cloves)
½ teaspoon saffron threads
Kosher salt and freshly ground black pepper
4 whole canned plum tomatoes, chopped
1½ cups half-and-half
1 cup heavy cream
2 tablespoons minced fresh parsley or dill