Step 1: Cook the Macaroni: Bring a large pot of salted water to a boil. Add the macaroni and cook according to package directions until al dente. Avoid overcooking, as the macaroni will soften further when mixed with the dressing.
Step 2: Drain and Cool: Drain the macaroni thoroughly and rinse under cold water to stop the cooking process and remove excess starch. This helps prevent the salad from becoming gummy. Allow the macaroni to cool completely.
Step 3: Prepare the Dressing: In a large bowl, whisk together the mayonnaise, apple cider vinegar, sugar, salt, and pepper until smooth. Adjust the sugar and vinegar to taste, ensuring a balance of sweet and tangy flavors.
Step 4: Adjust the Consistency: Gradually add milk, one tablespoon at a time, until the dressing reaches the desired consistency. The dressing should be creamy and pourable but not too thin.
Step 5: Combine and Chill: Gently fold the cooled macaroni into the dressing, ensuring that all the macaroni is evenly coated. If using, stir in the finely grated onion at this stage. Cover the bowl with plastic wrap and refrigerate for at least 2 hours, or preferably overnight, to allow the flavors to meld and the salad to chill thoroughly.
Step 6: Serve: Before serving, stir the mac salad to redistribute the dressing. Adjust the seasoning if necessary. Serve chilled alongside your favorite Hawaiian BBQ dishes.
Optional: For a richer flavor, use full-fat mayonnaise. A dash of yellow mustard can also be added to the dressing for extra tang. For a colorful variation, incorporate finely diced carrots or celery.