Combine breadcrumbs, parsley, onion, baking powder, salt, and pepper in a medium mixing bowl; stir until well combined. Add eggs, butter, and milk, stirring well.
Shape mixture by heaping teaspoonfuls into balls; place on baking sheets or plates. Cover and refrigerate at least 30 minutes or until ready to use.
Add balls to simmering soup or stew, allowing room for balls to expand during cooking. Reduce heat; cover and simmer 10 minutes. (Do not lift cover during cooking time.) Repeat procedure with remaining balls, if necessary.