Freeze cabbage heads for three days to soften leaves. Remove core and peel off 12-15 leaves, soaking them in warm water.

Cook rice in boiling water according to package instructions until al dente, about 15-20 minutes. Drain and cool slightly.

Sauté chopped onion in olive oil for 7-10 minutes until soft and translucent.

In a bowl, mix sautéed onions, ground beef, ground pork, cooked rice, parsley, carrots, salt, and pepper until well blended.

Whisk together crushed tomatoes, chicken stock, and sour cream in a separate bowl, seasoning to taste.

Cut thick stem off cabbage leaves. Place filling at the base, roll tightly, and place seam-side down in a greased casserole dish.

Preheat oven to 350°F (180°C). Pour some sauce at the bottom of the dish. Lay cabbage rolls in, add bay leaves, cover with sauce, and bake for 90 minutes.

After 90 minutes, uncover and bake for an additional 30 minutes to brown.

Let rest for 10 minutes before serving. Serve warm, drizzled with sauce.