Bring a large pot of salted water to a boil and cook the macaroni according to package directions until al dente—this is crucial for the right texture in the finished salad. Drain the pasta and rinse thoroughly with cold water to stop the cooking process and remove excess starch. Transfer to a large mixing bowl and set aside to cool completely while you prepare the other components.

While the pasta cools, finely shred the carrots using a box grater or food processor, and finely dice the onion. Add the shredded carrots, diced onion, and cider vinegar to the cooled macaroni, stirring gently to combine. Let this mixture chill for 15 minutes—this allows the pasta to absorb the vinegar's acidity, which brightens the overall flavor and prevents the final salad from tasting too heavy and mayo-forward. I find this step makes a real difference in balancing the richness of the mayo.

In a separate bowl, whisk together the mayonnaise, milk, sugar, and garlic powder until smooth and well combined. The milk thins the mayo to the right consistency and helps it coat the pasta evenly. Taste the dressing and adjust seasonings as needed—I like to add the salt and pepper now rather than at the end so the flavors integrate better throughout the salad.

Pour the creamy dressing over the macaroni mixture from Step 2 and stir gently until every piece of pasta is coated evenly. Cover the bowl with plastic wrap and refrigerate for at least 4 hours, or preferably overnight—this resting time allows the flavors to meld and the salad to develop its characteristic creamy, cohesive texture.

Remove the salad from the refrigerator and give it a good stir. If it seems too thick or the pasta has absorbed too much moisture, add a splash of milk (a tablespoon or two at a time) and stir until you reach the desired creamy consistency. Taste and adjust seasoning if needed, then serve chilled. The salad will keep well in the refrigerator for up to 3 days.