1. Bring a large pot of salted water to a boil, carefully cut the core from the cabbage, lower the whole head into the water, and simmer, peeling away outer leaves with tongs as they soften until you have 12 to 14 pliable leaves.

2. Lay the blanched leaves on a towel-lined tray to cool, and if any are very thick at the base, use a small knife to shave down the tough central vein so the leaf can roll easily.

3. In a large mixing bowl combine the ground beef, ground pork, cooked rice, finely diced onion, minced garlic, egg, chopped parsley, paprika, dried thyme, kosher salt, and black pepper, gently mixing with clean hands until evenly combined without compacting the meat.

4. To make the sauce, heat the olive oil in a wide skillet over medium heat, add the sliced onion, and cook until softened and lightly golden, then stir in the minced garlic just until fragrant.

5. Pour in the crushed tomatoes, beef broth, and tomato sauce, then add the brown sugar, red wine vinegar, kosher salt, black pepper, and bay leaf, stirring well and simmering for 10 to 15 minutes so the flavors meld.

6. Preheat your oven to 350°F (175°C) and spread a thin layer of the tomato sauce over the bottom of a large baking dish or Dutch oven.

7. Place one cabbage leaf on your work surface, add about 1/4 cup of meat mixture near the base, fold the sides in over the filling, and roll up tightly from the stem end to the top, repeating with remaining leaves and filling.

8. Arrange the stuffed cabbage rolls seam-side down in the prepared baking dish, nestling them snugly together in a single layer so they hold their shape while cooking.

9. Pour the remaining tomato sauce evenly over the rolls, making sure they are mostly covered, then cover the dish tightly with a lid or foil to keep the steam in.

10. Bake the cabbage rolls for 60 to 70 minutes, or until the meat is cooked through, the rice is tender, and the cabbage can be easily cut with a fork, adding a splash of extra broth if the sauce seems too thick.

11. Remove the dish from the oven, discard the bay leaf, and let the rolls rest for about 10 minutes so the juices settle and the rolls firm up slightly.

12. Serve hot, spooning plenty of tomato sauce over each portion and topping with a dollop of sour cream and a sprinkle of chopped fresh parsley.