Boil pasta in salted water until just tender (al dente). Drain and rinse under cold water to stop the cooking. Set aside.
Prepare the Dressing:
In a large bowl, mix mayonnaise, sour cream, Dijon mustard, vinegar, salt, and pepper until smooth.
Combine the Salad:
Add the cooled pasta, ham, cheddar, bell pepper, celery, and onion to the bowl with the dressing. Stir until everything is well coated.
Chill & Serve:
Cover and refrigerate for at least 1 hour for the flavors to meld. Before serving, give it a stir and adjust seasoning if needed. Garnish with fresh herbs if desired.