How to Make It
In a medium saucepan, cover the potatoes with cold water and boil gently over moderately high heat until tender.
Meanwhile, in a large skillet, combine the 3 tablespoons of vegetable oil with 1/2 teaspoon of the garlic and the rosemary. Cook over moderately high heat, stirring frequently, until the garlic is fragrant but not colored. Add the ground beef and break it up with a wooden spoon. Season the meat with salt and pepper and cook, stirring from time to time, until it is evenly browned. Empty the meat into a colander set over a bowl to drain off the fat. Transfer the meat to a large bowl.
In a small bowl, soak the bread in the milk for a few minutes; it should absorb as much as possible.
Drain the potatoes as soon as they are tender. Peel them while still hot and mash them through a food mill or ricer into the bowl with the meat. Add the milk-soaked bread and the remaining 1/2 teaspoon garlic, the parsley, 1 egg and the Parmesan. Mix thoroughly.
Break the remaining egg into a small bowl and beat it lightly with 2 tablespoons water. Spread the bread crumbs on a plate. Lightly roll the meat fixture into 1-inch balls. Dip the meatballs first in the beaten egg, lifting them out one at a time and letting any excess egg drip back into the bowl, and then roll them in the bread crumbs. Set the meatballs on a platter.
Pour 1/2 inch of vegetable oil into a large skillet and turn the heat to high; the oil is ready when a piece of bread added to the skillet sizzles immediately. Add as many meatballs as will fit loosely in the pan and fry, turning as necessary, until evenly browned all over, about 4 minutes. Adjust the heat as needed if the oil becomes too hot. Transfer the browned meatballs to a wire rack set over a try or paper towels. Fry the remaining meatballs in batches. Transfer the meatballs to a warmed platter and serve piping hot, or serve them at room temperature.