Discard the outer, dark green leaves from the savoy cabbage and then remove 8 leaves. Blanch the leaves in boiling salted water for 2-3 minutes, and then transfer to ice-water. Place leaves on paper towels and pat dry. Remove the hard core with a sharp paring knife.
Put 1 pound ground beef into a large mixing bowl and set aside. In a small skillet, sauté 1 chopped onion with 1 tablespoon olive oil. Transfer onions into a food processor. Add ½ cup breadcrumbs, 1 quartered tomato, ¼ cup chopped parsley, and 1 teaspoon Seven Spice blend; process to a coarse consistency.
Pour the mixture over the meat in the bowl, add one egg and mix gently together with your hands until evenly distributed (avoid over mixing).
Divide the mixture into 8 portions. On a clean work surface, place one savoy cabbage leaf, vein side up, and place one portion of the meat in the center. Gently shape into a round patty and fold the sides of the leaves around it.
Repeat with the remaining meat and leaves. Place the cabbage rolls into a large iron skillet or a baking dish. If using, arrange the potato and tomato slices upright between the rolls.
Preheat oven to 375 degrees Fahrenheit.
For the sauce:
In a small bowl or a cup, combine the 2 cups broth or water with 2 tablespoons tomato paste, 1tablespoon olive oil, 1 teaspoon Seven Spice blend, one teaspoon salt, and 2 teaspoons black pepper. Pour the sauce over the cabbage rolls, cover with aluminum foil and bake in the oven for 30 minutes. Remove the foil and return to the oven for 15 minutes or until potatoes have started to brown (if using).