Add the onion, garlic, rosemary, 1 teaspoon of salt and two tablespoons of the tomato paste to the pot and stir to combine. Allow to thicken slightly, about two minutes. Return the meat to the pot and pour tomatoes over the top of the meat. Stir and then add the stock.
Remove from the oven and allow to cool for 15-20 minutes. Remove the parmesan rind from the sauce and discard. Remove the rosemary stems and discard. Puree sauce with an immersion blend until desired consistency is reached (you can also do this with potato masher if you do not have an immersion blender). Add salt to taste.