01 - Bring a large pot of salted water to a boil. Add elbow macaroni and cook until very soft, about 1-2 minutes longer than package instructions for al dente. Drain well and allow to cool slightly.
02 - In a large mixing bowl, whisk together mayonnaise, milk, apple cider vinegar, sugar, salt, and black pepper until smooth.
03 - While macaroni is still warm, add to the dressing and toss to coat thoroughly.
04 - Stir in grated carrots, chopped celery, onion, and green onions. Mix until evenly combined.
05 - Cover and refrigerate for at least 2 hours, or overnight for best flavor and texture. Before serving, check for seasoning and add more mayonnaise or milk if needed for creaminess.