Heat the oven to 350°F. Soak the bread in the milk until soggy, about 5 minutes. Squeeze the liquid from the bread and combine the bread gently with the meat, onion, Parmesan, parsley, and some salt and pepper. Shape into 1/2-inch meatballs, pressing no more than is necessary.
Put the oil in a large pot or Dutch oven over medium heat for 1 minute. Add the meatballs and cook, turning once or twice, until well browned and firm, 5 to 10 minutes total; as they finish cooking, remove them with a slotted spoon.
Add the garlic to the pot and cook, stirring, until soft, about 5 minutes. Add the rice and stir until glossy and coated with oil, about 1 minute more. Add the white wine and let the liquid bubble away. Add the stock, escarole, meatballs, and a sprinkling of salt and pepper. Bring to a boil.
Cover and bake, undisturbed, for 30 minutes. Remove the cover and test a grain of rice. It should be almost tender but not quite ready; if it’s still too tough, check to make sure there’s some water left in the bottom of the pot, cover again, and bake for another 10 minutes. When the rice is done, remove the pot from the oven and let it rest for at least 5 minutes or up to 15 minutes. Taste and adjust the seasoning. Serve.