http://homesicktexan.blogspot.com/2009/06/buttermilk-dressing.html

butter-milk dressing...

for everyone that thinks this beautiful bliss comes from a dry package or bottle...you will love the flavor and simplicity, and you can tailor the flavor profile or consistency to your own taste...

Buttermilk dressing, extra spicy
  
Ingredients:
1/4 cup of mayonnaise
1/2 cup of sour cream
1/2 cup of buttermilk
1/4 cup of chopped cilantro
1 tablespoon of freshly squeezed lime juice
1 clove of garlic, crushed
1 serrano pepper, finely diced
1 teaspoon of chopped fresh chives
1/8 teaspoon of cayenne pepper
Salt and black pepper to taste

Method:
Mix all the ingredients together and let chill for an hour.
Makes 1 cup, keeps for a week in the refrigerator.
Notes: I like my dressing on the thinner side, so if you prefer it thicker use 1/2 cup of mayonnaise. And if you don't want it to be so spicy, feel free to omit the Serrano or substitute a jalapeno pepper instead. Also, you can use parsley instead of cilantro if you're one of those "Cilantro tastes like soap" people, I won't be insulted.

i omit the cayenne...but, you can add more mayo or sour cream, less buttermilk for a tighter consistency (but i love buttermilk...not necessarily to drink, but you can't beat in for cooking -  cakes, pancakes are tender, fried chicken - dip or soak in butter milk and dredge in coating...and these types of dressings or dips...yum)...play with it, this is a great start...

plus, it's good on everything, veggies, chips, fries, pizza, burgers, wings, tacos, fish, beef...and on and on and on...