Cook the pasta until it is very soft in plenty of boiling, salted water (4 quarts). Go over the box directions' cook time by about 50%, then drain well and transfer to a large bowl. Example: If the box says 10 minutes, then it should cook for about 15 minutes.
Pour the vinegar into the pasta and stir to combine. Cover and let sit for 20 minutes.
While the pasta sits, make the dressing by whisking the mayonnaise, milk, mustard and sugar in a small bowl until the sugar fully dissolves. Taste test and adjust acidity levels by adding a little more sugar or some cider vinegar as needed. Season with salt and pepper. Reserve 1 cup of the dressing to add right before serving.
Add the veggies and the dressing to the pasta. Gently stir to fully combine.
Cover and refrigerate for at least an hour or overnight to chill.
Just before serving, stir in the reserved cup of dressing until fully combined and garnish with some scallions. Enjoy!
Notes
This recipe can easily be scaled up or down.
The brand of mayo makes a big difference. Use Best Foods or Hellmann's
Reserve 1 cup of the dressing and add right before serving, whether that be an hour after chill or the next day. This will freshen up the mac salad with fresh dressing.
You can substitute lemon juice for vinegar if needed.
Get all ingredients out and mise en place prep ahead so it is super easy to make.
Lasts for up to 3 to 5 in the refrigerator but is best within the first 2 days.