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. Be careful not to overcook.
Step 2: Rinse and Cool: Drain the macaroni immediately and rinse thoroughly with cold water to stop the cooking process and remove excess starch. Drain well and transfer to a large mixing bowl. Allow the macaroni to cool completely.
Step 3: Prepare the Dressing: In a separate bowl, whisk together the mayonnaise, white vinegar, sugar, salt, and pepper until smooth.
Step 4: Combine and Mix: Pour the dressing over the cooled macaroni. Add the diced onion and celery (if using). Gently mix until the macaroni is evenly coated with the dressing.
Step 5: Adjust Consistency and Flavor: Add milk, a tablespoon at a time, until the salad reaches your desired consistency. Taste and adjust seasoning as needed, adding more salt, pepper, or sugar to your preference.
Step 6: Chill: Cover the bowl and refrigerate for at least 2 hours, or preferably overnight, to allow the flavors to meld. The salad will thicken as it chills.
Step 7: Serve: Before serving, stir the salad well. If it seems too thick, add a little more milk to loosen it up. Serve cold and enjoy!
Optional Tips: For a richer flavor, use a full-fat mayonnaise. If you prefer a tangier salad, add a little more vinegar. Some cooks add a pinch of MSG (Accent) for an umami boost. Other variations include adding shredded carrots, tuna, or a splash of soy sauce.