First of all we have to prepare cabbage leaves. To do that, take cabbage leaves and then wash & dry with paper towel and put in boiled water with vinegar and 1 tsp of salt for 1-2 minutes, depends how hard these cabbage leaves are. After that immediately place it in cold water to stop the process of cooking. Therefore cabbage will become soft and elastic. I suggest to remove the hard part of a leave also to make stuffing easier.
Now lets prepare stuffing – rice and vegetables. Chop nicely onion and garlic, wash and cut mushrooms into small pieces and grate the carrot. Heat frying pan with olive oil and when its hot enough start frying onion and garlic until golden. Then add carrot and mushrooms and keep frying until its ready.
Mix the half cooked rice with vegetables nicely and then add salt and pepper as per your taste. Now take one cabbage leaf and place stuffing in the middle and wrap like an envelop. If you can’t do it from the beginning i advice to use wooden toothpicks.
When you are finished stuffing cabbage leaves then place our Golubtsi in a pot with wide bottom or in a deep frying pan. Pour water and tomato paste and salt again if needed. Cover with a lid and cook on a low flame for 30-40 minutes. Water should dissolve and tomato paste become thick.
Try it out. Let me know in comments about your experience.