Preheat the oven to 180 degrees C. To prepare the meatballs, mix the beef in a large bowl with the breadcrumbs, onion, carrot, parsley, milk, marjoram, salt, sage, pepper and lightly beaten egg. Shape the mixture into a 2.5-cm-thick rectangle and cut into 18 pieces. Roll each piece into a ball. Place the meatballs in a large baking pan and bake for 15–20 minutes, or until the meatballs are no longer pink. Drain on paper towels.
Meanwhile, prepare the sauce. Whisk the apple juice, brown sugar, vinegar, cornflour, soy sauce and garlic together in a medium saucepan. Bring to the boil, stirring frequently, and cook for 2 minutes, or until thickened. Stir the meatballs into the sauce and simmer for 3 minutes, or until heated through.
To serve, place the meatballs in a small chafing dish or shallow serving dish and provide cocktail forks or toothpicks.