Cook the pasta according to package directions until al dente. Drain the pasta and rinse immediately with cold water to stop cooking and cool it down. Set aside.
In a large bowl, combine the cooled pasta, cooked shrimp, and flaked crab meat.
In a separate medium bowl, whisk together the mayonnaise, sour cream, lemon juice, Dijon mustard, dried dill weed, salt, and pepper until the dressing is smooth.
Add the chopped celery and red onion to the seafood and pasta mixture.
Pour the dressing over the salad ingredients. Gently fold everything together until the pasta and seafood are evenly coated. Do not overmix.
Cover the bowl and refrigerate the seafood pasta salad for at least 2 hours before serving. This allows the flavors to blend.
Before serving, taste and adjust seasoning if needed. Garnish with fresh parsley.
Notes
For the best texture, make sure the pasta is completely cold before mixing with the dressing.
If you prefer a lighter dressing, substitute half the mayonnaise with plain Greek yogurt.
This make ahead seafood salad tastes best when chilled for several hours.