Heat 2 tablespoons olive oil in large skillet over medium-high heat and arrange pork belly, fat- side-down, and brown on all sides.
Heat remaining 2 tablespoons olive oil in heavy-duty oven-proof saucepot over low heat and cook onion with garlic to caramelize. Stir in Knorr® Homestyle Stock - Beef and cider. Bring to a boil over high heat. Stir in pork belly and 4 sage leaves. Cover tightly with aluminum foil, then cover with pot lid. Bake covered 2 hours or until pork is tender.
Meanwhile, brown cipollini onions in remaining 2 tablespoons olive oil over medium heat in another skillet. Add remaining 4 sage leaves and cook just until wilted. Reserve for garnish.
Remove pork to serving dish and garnish with onions and sage. Pour cider mixture over pork.