Vegetarian Polish stuffed cabbage rolls packed with seasoned white rice, wild forest mushrooms, and sweet caramelised onions, baked in a rich, sweet-tart tomato sauce.
Cut the core out of the cabbage. Submerge the whole head into a large pot of boiling water. As outer leaves soften after 2 to 3 minutes, peel them off carefully with tongs onto a plate. Trim down the thick central vein on each leaf so it rolls easily.
Sauté the diced onions in butter until golden brown. Add the diced mushrooms and cook for 6 minutes until their moisture has evaporated. In a large bowl, mix the sautéed mushrooms and onions with the cooked rice, marjoram, salt, and pepper.
Place two tablespoons of mushroom-rice filling near the stem end of each cabbage leaf. Fold the sides in tightly over the filling, then roll up into a neat, firm parcel.
Line the bottom of a casserole dish with leftover cabbage leaves. Pack the rolls tightly in layers, seam-side down. Whisk the passata with vegetable broth, season with salt and pepper, and pour over the rolls. Cover with foil and bake at 180°C (160°C fan) for 50 minutes until tender.