Step 1

Bring 4 quarts of water to the boil. Add a teaspoon of salt and the macaroni and cook until very soft, for 15 minutes. Drain well and return to the pot. Stir in the vinegar, tossing well, then let stand 10 minutes to cool.

Step 2

In a medium bowl, combine 1½ cups of the milk and 1 cup of the mayonnaise with the brown sugar. Whisk into the cooled pasta and toss, adding salt and pepper.  In a small bowl, combine the remaining ½ cup milk with the remaining 1 cup mayonnaise, stir in the green onions, carrot, and celery and toss with the pasta until well coated. Cover and chill for at least 1 hour before serving. Taste and add additional salt and pepper as desired.