Cut out the core of the cabbage and carefully remove the leaves. Bring a large saucepan of salted water to the boil and simmer the leaves 10 minutes then drain.
Dip the bread roll in water to soften it and squeeze the water out. In a bowl, combine the bread, beef mince, pork mince, egg, diced onion, salt and pepper and caraway. Mix well.
Place about 3 tablespoons of the mixture on a cabbage leaf and roll up, tucking in the ends. You can pin them with toothpicks but it isn't really necessary.
Preheat the oven to 180 degrees C. Lay the bacon rashers over the bottom of a deep heavy saucepan and layer the cabbage rolls on top. Top with sliced onion and pour over the beef stock. Bake, covered, 1 hour.