Make a few slices on the outside of the veal shanks so they retain their shape during cooking. Dredge the veal shanks in flour, ensuring that they are evenly coated.
Melt the butter in a large skillet over medium heat. Add the veal shanks and season with salt and pepper. Brown well on both sides, remove and set aside. In the same skillet, add the sliced onion and brown. Return the veal shanks to the skillet. Add the white wine and allow to evaporate.
Cover the veal shanks with broth and simmer for an hour and a half, covered.
Prepare the gremolata: finely chop the peeled garlic, parsley, lemon zest and rosemary. Sprinkle the veal shanks with this mixture immediately before serving.