Begin by boiling water and cooking the rotini according to package instructions. Once done, drain the pasta and rinse under cold water until it’s completely cooled — this prevents it from continuing to cook and helps keep the salad refreshing. Shake off excess water so the salad won’t get watery.
While pasta cooks, cut the broccoli florets into bite‑sized pieces — avoid the tough stalks, since raw broccoli stays crunchy. Finely chop the red onion and shred the cheddar cheese.
In a small bowl, whisk together the mayonnaise, sour cream, sugar, and apple cider vinegar until smooth and creamy. If you like, add salt and pepper to taste.
In a large bowl, toss together the broccoli, shredded cheddar, and chopped onion. Pour in the dressing and gently mix so everything gets coated. Once pasta is cooled and drained, add it to the bowl and toss again until pasta, veggies, and cheese are evenly coated.
You can serve the salad right away, but I find it tastes best after chilling in the fridge for at least one hour — it helps the flavors meld and gives a cooler, crisp texture.