Bring about 3 litres of water to a rolling boil in a large pot and stir in the 1 tbsp of kosher salt. Add the 250g of elbow macaroni and cook it 2–3 minutes longer than the package al dente timing, usually about 12 minutes in total, until the pasta is very tender and soft but still holds its elbow shape. Drain thoroughly in a colander, shaking off the excess water, and do not rinse. The macaroni should look plump and slightly swollen, with no firm bite left in the centre. That extra cooking, combined with the surface starch left on the unrinsed pasta, is what lets the dressing cling and keeps the finished salad creamy.

Tip the hot drained macaroni straight into a large mixing bowl and immediately toss it with the 2 tbsp of apple cider vinegar. Leave it for 10–15 minutes, stirring once or twice, until the vinegar has soaked in with no liquid pooling at the bottom of the bowl and the pasta has cooled to just warm. Use this time to grate the carrot and mince the onion. The pasta should smell lightly tangy rather than sharply sour. That warm absorption is what builds the gentle, characteristic tang inside each piece, which vinegar stirred into cold dressing could never match.

In a separate large bowl, whisk together the 240g of mayonnaise, 60ml of whole milk, the 2 tbsp of sour cream or Greek yogurt if using, 1 tsp of sugar, ½ tsp of kosher salt and ½ tsp of black pepper until completely smooth. Stir in the 60g of finely grated carrot and 40g of very finely minced or grated onion. The dressing should look slightly loose and pourable at this stage rather than stiff or paste-like. That looseness is deliberate, because the macaroni keeps absorbing dressing as it chills and a dressing that starts thick finishes dry.

Add the dressing to the slightly cooled macaroni, making sure the pasta is only just warm so the mayonnaise does not turn oily, and fold gently but thoroughly until every piece is evenly coated. Taste and adjust with a little more kosher salt or black pepper if needed. The pasta should look heavily coated and glossy, genuinely creamy rather than dry. If it already looks stiff, fold in 1–2 tbsp of whole milk. That generous coating matters because the macaroni will pull dressing into itself throughout the chill.

Cover the bowl and refrigerate for at least 1 hour, so the macaroni can absorb flavour and the dressing can settle. Before serving, stir the salad well. If it has tightened, loosen it with a small splash of milk and, if needed, 1–2 tbsp of extra mayonnaise, then finish with freshly cracked black pepper. The final texture should be creamy and spoonable, never dry or tight. That brief refresh is what returns the salad to its proper consistency after the pasta has finished absorbing.