Remove core from cabbages. In a large pot bring water to a boil, enough to almost cover the cabbage. Add salt, few thyme and dill sprigs. Immerse cabbage in boiling water with core side down. Cook over medium-high heat 5 to 10 minutes. Turn and gently remove leaves. When the leaves are tender and flexible remove and let them cool. 

Prepare the filling. In a frying pan heat oil over medium high heat. Cook onion until soft and glossy. Stir in paprika and tomato paste and remove from heat. Let cool slightly. Add rice, ground pork and beef, dill, salt and pepper. Stir until well combined.

Trim the thick veins from cabbage leaves for easier rolling and set aside. Cut leaves in smaller pieces if too large. Chop any leftover cabbage (middle part) and the veins and place in a bowl. Mix chopped cabbage with dill, salt and pepper. Place few thyme sprigs on the bottom of a large pot, place half of the chopped cabbage and few dill sprigs on top.

Start making the cabbage rolls. Place 1/2 to 1 tablespoon of mixture on the center of the bottom of each leaf. Fold in the sides and start rolling the cabbage leaf to create a roll.Place on the prepared pot and continue until all the filling is done. Place the other half of chopped cabbage over the top of the rolls.

Add diced tomatoes on top, arrange the pork ribs and pour hot salted water until the cabbage rolls are almost covered with liquid.

Cover the pot and cook at medium heat until they start to boil. Reduce heat to low and simmer for 1 hour.

Serve cabbage rolls warm with sour cream and polenta.