1. Combine in a large bowl beef, pork, onion and a mixture of flour, salt, and pepper.
2. Add gradually, mixing vigorously milk, water and egg.
3. Beat vigorously until mixture is smooth and well blended.
4. Heat butter in a heavy skillet.
5. Using a tablespoon (not measuring spoon), drop the meat mixture by rounded tablespoonfuls into the skillet. (Meat will drop more readily from a spoon dipped in melted butter.) Cook over medium heat until browned. Using a slotted spoon turn meat balls to brown evenly. Allow about 8 to 10 min. to cook meat balls.