Season the beef shanks with salt and pepper. Heat a large skillet over medium heat and brown the shanks on all sides, then transfer them to the slow cooker.
Add the carrots, onion, celery, and garlic to the slow cooker. Pour in the white wine, beef broth, and diced tomatoes. Add the thyme and rosemary.
Cover and cook on low for 8 hours until the beef is very tender.
About 30 minutes before serving, start the risotto. Melt the butter in a saucepan over medium heat and cook the remaining chopped onion until soft.
Add the arborio rice and stir for 1 minute. Gradually add the chicken broth one cup at a time, stirring often and waiting until each cup is absorbed before adding the next.
Once the rice is creamy and tender, stir in the parmesan cheese. Serve the risotto alongside the beef shanks and sauce.