Start by heating the beef tallow (or the butter) in a cast iron pan over high heat. Once the butter melts, add the beef shanks and brown them on both sides.
Pour the broth over and season with salt and black pepper.
Bring to a simmer. Then, if you want to cook on the stovetop, reduce the heat and cover with a lid. Cook on low heat for 3 to 3.5 hours until the meat is tender.
If you want to cook in the oven, after it simmers place the lid on and bake for 2 to 2.5 hours until the meat is tender.