In a medium bowl whisk together the half-and-half, mayonnaise, grated onion, dark brown sugar, 1 teaspoon of salt, and 2 teaspoons of pepper until smooth.

Refrigerate until needed.

Cook the macaroni as per the package instructions, except add 5 minutes to the cooking time on the package instructions (you want the macaroni to be very soft and plump so it absorbs the dressing better).

Drain the macaroni into a colander and then dump it back into the pot.

Add in the apple cider vinegar and stir until the pasta absorbs the vinegar.

Cover the pot with a lid and cool for 20 minutes at room temperature.

Add half of the dressing and stir to combine.

Then, cover the lid and cool for another 20 minutes.

Add the remaining dressing, green onions, celery, and carrots to the pot and stir to combine, and season with salt and pepper if needed.

Cool completely to room temperature, for about 30 more minutes.

Transfer the macaroni salad to a bowl and cover with plastic wrap.