(After trying to take a photo of the ranch in my Kitchen Aid and failing miserably, I resorted to our taco salads...)
1 quart buttermilk
30 oz container of mayonnaise (or 2 quarts if you want it thicker)
2 teaspoons onion salt
1/2 teaspoons garlic powder
1 teaspoon salt
3/4 teaspoons pepper
2 teaspoons dried parsley
Add together. When adding the parsley rub it together in your palms to make it finer. Blend until smooth. Makes 2 quarts.
Note: Compared to Hidden Valley Ranch, it's a pretty thin recipe. That's part of the reason why I love it... you can pour a little amount all over your salad, and you don't ever have any bites with tons of dressing. Regardless, if you like your ranch thick - add more mayo.