Cook pasta to al dente according to package directions in heavily salted water. Drain pasta, rinse under cold water until cool. Set aside.
While the pasta cooks, soak the sliced onion in ice water for 5-10 minutes. Drain and set aside.
In a small bowl, whisk together mayonnaise, sour cream, ranch seasoning, apple cider vinegar, salt, and pepper.
In an extra large bowl, toss together the pasta, about ¾ of the dressing, lettuce, tomatoes, bacon, and onions.
Cover and chill for 2 hours. Just before serving, toss with a few more tablespoons of the dressing. Taste and adjust seasoning as needed.
