Prepare the Cabbage: Bring a large pot of water to a boil. Remove the core from the cabbage and carefully place the head in boiling water. Blanch for a few minutes until the leaves become tender and can be peeled off easily. Retain half a cup of the leftover water for your sauce.
Mix the Filling: In a large bowl, combine the cooked rice, ground beef, Worcestershire sauce, egg, minced onion, parsley, garlic, salt, black pepper, dill, onion powder, and chili flakes (if using). Mix with your hands or a spoon until well combined.
Form the Rolls: Lay a cabbage leaf flat and place a heaping tablespoon of filling near the base. Fold the sides over the filling and roll it up tightly, tucking in the ends as you go. Repeat this process with the remaining leaves and filling.
Assemble in a Baking Dish: Preheat the oven to 350°F (175°C). Spread a thin layer of tomato sauce in a large baking dish. Arrange the cabbage rolls seam-side down in the dish. Pour the remaining tomato sauce and reserved water over the top.
Bake: Cover the dish with foil and bake for about 1 hour. Remove the foil for the last 15 minutes to allow the tops to brown slightly.
Serve and Garnish: Once cooked, allow the rolls to sit for a few minutes before serving. Garnish with fresh dill if desired.