1. Peel the onion and garlic and cut in half. Place in the bowl fitted with the ultrablade knife and mix at speed 12 for 10 seconds. Scrape down the sides of the bowl with a spatula.
2. Replace the ultrablade knife with the mixer and add the oil. Launch the P1 simmer program at 270°F for 5 minutes. Place flour and lamb shanks in a plastic bag, shake to coat evenly. Peel and thinly slice the carrot. Thinly slice the celery and mushrooms.
3. Place the lamb, carrot, celery, mushrooms, diced tomatoes, broth, salt and pepper in the bowl. Launch the P2 simmer program at 200°F for 2 hours, stirring occasionally to make sure shanks are evenly placed.
4. Transfer lamb and sauce to a serving dish, stir in parsley.