Remove the stalk from the savoy cabbage and take off the outer leaves. Boil the outer leaves in salted water for 2-3 minutes and then plunge them in ice water. Dab the leaves with a paper towel. Line a bowl with plastic wrap and place a layer of savoy cabbage leaves in it.
Cut the savoy cabbage innards, carrot, bell peppers, onion, and garlic into small pieces and saute everything in a skillet with some olive oil. Season with fennel seed, salt, and pepper. Transfer the medley to a bowl and let cool.
Add the ground beef, eggs, shredded mozzarella, parsley, salt, and pepper to the bowl and combine well. Now transfer about ⅓ of the mixture to the bowl with the plastic wrap and cabbage leaves.
Now alternate layers of savoy cabbage and the ground beef mixture in the bowl, with the last layer being savoy cabbage. Close the plastic wrap around the stuffed cabbage so that it's in the shape of a ball and refrigerate for at least 2 hours.
Preheat the oven to 350°F and lay out the cooking twine like a spider web. Remove the plastic wrap from the cabbage and place the stuffed head in the middle of the cooking twine. Knot the twine at the top and cut off the excess string. Place the stuffed cabbage in a stock pot and add 2 quarts of warmed broth. Place the lid on the pot, transfer the pot to the oven, and cook for 60 minutes. Let the stuffed cabbage cool, remove the cooking twine, serve with tomato sauce, and dig in!