Preheat the oven to 350°F.
Cabbage. Fill a large pot with water and bring it to a boil, then season generously with salt. Core the cabbage and remove the outer leaves. You’ll need about 20 cabbage leaves. Working in batches, blanch the leaves in the boiling water for about 5 minutes or until tender. Drain well and arrange them in a single layer on a paper towel-lined baking tray to cool.
Filling. Heat the olive oil in a large cast iron pan over medium heat. Cook the onions and carrots until softened, 2 minutes. Add the ground beef, sausage, garlic, thyme, bay leaf, allspice, salt and pepper. Cook until the meat is browned and cooked through.
Add in the crushed tomatoes and simmer for 5 minutes. Remove the pan from the heat and let cool. Discard the thyme and bay leaf. Add the egg and mix.
Assemble. Butter a 7-inch souffle dish. Line with blanched cabbage leaves, allowing a few inches to hang over the edges. Spoon in ⅓ of the meat filling.
Cover the filling with 2-3 cabbage leaves, then brush with melted butter and season with salt and pepper. Repeat this process two more times. Fold the overhanging cabbage leaves into the center.
Cooking. Bake for 45 minutes or until the internal temperature reaches 165°F. Remove from the oven and let rest for 15 minutes. To unmold, place a plate over the souffle dish, flip the plate and dish, and remove the mold. Cut into slices and serve.