Boil rotini pasta according to package directions for al dente, adding one tablespoon kosher salt to the cooking water, if desired. Drain well and run a little bit of cold water over the pasta. That will help cool the pasta and stop the cooking process. Pat dry with paper towels and set aside.
In a separate, large bowl add the mayonnaise, sour cream, buttermilk, dry Ranch dressing mix, garlic powder, and salt and black pepper. Mix well until a creamy, blended dressing forms.
In another large salad bowl, add the cooked pasta, frozen peas, and diced ham. Pour the dressing over the pasta mixture. Stir well, being sure everything is coated in the dressing.
Can be served immediately, but is best when it can set in the refrigerator for an hour or two before serving.
Notes
Be sure pasta is very dry before adding the dressing.