Peel the tomatoes, remove the seeds and then grate them on a box grater. Rinse the meat and dry it, then add salt and pepper. Put it in a clay baking dish with a cover and add the garlic, olive oil, tomatoes, bay leaf and tomato puree dissolved in a bit of warm water.
Cover the dish and cook at 180οC for 1½ hour. Sauté the onions in the butter for 2-3 minutes until they wilt. Remove the baking dish from the oven, add the orzo, onions and hot water. Continue to cook (with the cover on) for 1 hour more. Add hot water if necessary.