Cook the Pasta: Bring a large pot of salted water to a boil. Introduce the pasta to boiling water and cook according to the package directions until it reaches an al dente texture. Once done, drain the pasta and rinse it under cold water to halt the cooking process. Set it aside for later use.

Prepare the Dressing: In a large mixing bowl, whisk together the mayonnaise, sour cream, Dijon mustard, white vinegar, lemon juice, sugar, salt, and black pepper until smooth and creamy.

Add the Vegetables: To the bowl with the dressing, add the chopped red and green bell peppers, red onion, celery, parsley, and optional black olives and Parmesan cheese. Stir to combine.

Combine and Toss: Add the cooled pasta to the bowl and gently toss until the pasta is well coated with the dressing and mixed with the vegetables. Adjust seasoning to taste, adding more salt or pepper if needed.

Chill and Serve: Cover the bowl and refrigerate for at least 1 hour to let the flavors meld together. Give the pasta salad a quick stir before serving and garnish with extra parsley if desired. Serve chilled.