Steam the rice and cabbage head separately. Set the steamed rice aside. Peel off the cabbage leaves to have individual leaves.
Add chopped onion, oil, bouillon, and the steamed rice to the ground pork meat. Mix together. Season with salt and pepper. Roll the ground pork mixture into golf ball-sized balls. Wrap each pork ball in a cabbage leaf.
Add carrots and celery into the baking pan (vegetables prevent the cabbage from burning onto the bottom of the pan, and also adds an aroma to the rolls) and arrange the cabbage rolls on top.
Place the pan into the oven and cook for about 1 1/2 hours. Check if it is thoroughly cooked before removing from the oven.