Bring a pot filled with water to boil. Add in salt and put the cabbage leaves into the pot. Cook them for 3-4 minutes or until they are slightly tender. Drain and transfer the leaves into a large bowl with cold water to stop cooking.
Mix all the ingredients for the filling until combined well.
Remove the very thick stems of the cabbage leaves using a knife so that you can roll them up easily.
Put some filling on the leaves and roll them up. If the leaves are too long, just cut them into two or three after they are stuffed and rolled up.
Place a few large cabbage leaves at the bottom of a pot and place the rolls on them. If there is any juice left from the filling, just pour it over them. Cook them for about 10 minutes and then pour 1 cup of hot water, cover the pot and cook for about 40 minutes or until tender.
Meanwhile you can prepare the casserole sauce. Dissolve tomato paste in hot water and add in olive oil, minced garlic, salt and vinegar.
Preheat oven to 200C.
Transfer the rolls into a baking pan. Don’t leave the water in the pot, pour it into the pan too. If you cook the rolls in an iron cast pan, no need for that transfer. You can just bake it in the same pan.
Pour the tomato sauce over the cabbage rolls and bake for about 20 minutes, until the rolls get brownish.
Remove it from oven, top with shredded mozzarella and bake for another 10 minutes or until the cheese melts.