Bring a large pot of salted water to a boil. Add the pasta and cook according to package directions until al dente, usually about 8-10 minutes.

While the pasta cooks, prepare an ice bath by filling a large bowl with cold water and ice. Drain the cooked pasta and immediately transfer it to the ice bath to stop the cooking process. Let it cool for 2-3 minutes, then drain well and set aside.

Bring another pot of water to a boil. Add the broccoli florets and blanch for 1 minute exactly—this keeps them crisp and bright green. Quickly drain the broccoli and transfer it to the ice bath to cool. Drain again and pat dry with a clean kitchen towel.

In a large mixing bowl, whisk together the mayonnaise, sour cream, apple cider vinegar, Dijon mustard, garlic powder, salt, and pepper until smooth and well combined.

Add the cooled pasta, blanched broccoli, and chopped red onion to the bowl with the dressing. If using, add the sunflower seeds and dried cranberries.

Gently toss everything together until evenly coated with the dressing. Taste and adjust seasoning with more salt or pepper if needed.

Cover the bowl with plastic wrap or transfer to an airtight container. Refrigerate for at least 1 hour to allow the flavors to meld. Stir once before serving.