In a large braising dish with a lid, heat the sugar to a dark caramel color, shaking the pan occasionally for even cooking. Add the vinegar and cook for 3 minutes. Add the scallions, ginger, garlic, soy sauce, beef broth and star anise. Place the beef shanks in the pot, ensuring that there's enough liquid to come halfway up the sides of the meat, and cover tightly with a lid. Braise in the oven for 3 hours, until the meat is falling-apart tender.
Melt the butter in a large skillet. Sauté the onion and garlic until soft, about 7-10 minutes. Add the rice and cook, stirring, until opaque, about 4-6 minutes. Add 1/2 cup chicken broth and bring to boil. Reduce to a simmer and continue to add the chicken broth in 1/4 cup increments, stirring constantly. Only add the next addition of broth when the previous one is fully absorbed. Fold in the peas and parsley.
Divide the risotto between bowls and serve with braised beef on top.