Cook the pasta. Bring a large pot of salted water to a boil. Cook the pasta until just al dente according to package directions. Drain and rinse under cold water to stop the cooking and cool it down.
Crisp the bacon. While the pasta cooks, fry the bacon in a skillet over medium heat until crisp.
Drain on paper towels and crumble when cool. Reserve 1–2 teaspoons of bacon drippings if you like for extra flavor in the dressing.
Whisk the dressing. In a large bowl, whisk mayonnaise, sour cream, buttermilk, ranch seasoning, Dijon, vinegar or lemon juice, garlic powder, pepper, and a pinch of salt. If using, whisk in a bit of the cooled bacon drippings for a smoky note.
Toss the pasta. Add cooled pasta to the bowl with the dressing.
Fold gently to coat every piece. This first toss helps the pasta absorb flavor without drying out.
Add the mix-ins. Stir in bacon, tomatoes, peas or corn, red onion, celery, cheese, and herbs. Taste and adjust seasoning with more salt, pepper, or ranch mix as needed.
Chill to set. Cover and refrigerate for at least 30–60 minutes.
This helps the flavors meld and the dressing thicken slightly.
Finish and serve. Before serving, give it a gentle stir. If the salad seems a bit thick, loosen with a splash of buttermilk or milk. Top with a little extra bacon and herbs for a fresh finish.