Place shin beef in a kettle with plenty of water (never add more). Let boil hard for 5 minutes, then turn down heat to medium. Add can of tomato puree, chopped onions, celery, parsley, and a pinch of thyme; salt and pepper to taste.
Cover and let simmer several hours. One hour before serving, add a good handful of rice and a bag of frozen mixed vegetables.
Have bones at room temperature. Empty marrow into bowl. Add salt and pepper, chopped parsley, and 2 eggs. Using electric mixer, beat together until smooth.
Starting with 1/2 cup, add bread crumbs until slightly firm. Form into balls and refrigerate 3/4 hour before serving. Add gently into simmering soup one at a time and turn over carefully when half done.