Taste a small piece of fermented cabbage. If it's very salty, rinse the leaves briefly under cold water and drain well. Carefully trim the thick central ribs to make the leaves easier to roll, keeping them intact. Reserve the trimmings for lining the pot.
Heat the oil in a skillet over medium heat. Add the chopped onion and cook for about 8 minutes, until softened. Let cool, then combine with the ground beef, ground pork, rinsed uncooked rice, paprika, and black pepper. Mix well and divide the filling into 12 equal portions.
Place a portion of filling near the stem end of each cabbage leaf. Fold in the sides and roll snugly, leaving a little room for the rice to expand during cooking.
Line the bottom of a large, heavy-bottomed pot with the reserved cabbage trimmings. Arrange the cabbage rolls seam-side down in snug layers, adding the sliced bacon and bay leaves between them.
Pour in the water and place a small, heatproof plate over the rolls to keep them in place during cooking. Cover the pot with a lid.
Bring the liquid to a gentle simmer and cook over low heat for approximately 2 hours. Add a little hot water if needed to keep the rolls almost covered. The sarma is ready when the rice is tender and the filling reaches an internal temperature of 167°F (75°C).
Remove from the heat and let the cabbage rolls rest, covered, for 20 minutes. Serve three rolls per person, spooning a little of the savory cooking broth over each portion.