Coat a large saute pan with olive oil and put the pan over medium heat. Add the onions, season with salt, to taste, and saute until they are translucent and aromatic but have no color, about 5 to 6 minutes. Add the garlic and cook for 2 to 3 more minutes. Remove from the heat and cool.
In a large bowl, combine the meats, rosemary, Parmesan, water, bread crumbs, and eggs. Season generously with salt and add the cooked onions and garlic. Combine until well mixed. (Squish with your hands, it's fun!)
Make a small patty of the meat mixture. Cook it and eat it. This is a tester patty to check and see if the seasoning is correct (it will probably need salt). Adjust the seasoning, if needed.
Roll the meat mixture into 3/4-inch meatballs. Coat a large saute pan with olive oil and put over high heat. Working in batches, cook the polpettini until they are brown on all sides. Add half a cup of chicken stock and cook until the stock has reduced by half. Remove to serving platters. Repeat this process until all the polpettini are cooked and serve immediately. Buonissimo!