In a medium mixing bowl, stir together the sour cream, mayonnaise, ranch dip packet, and garlic salt.
In a blender or food processor, puree the cilantro and pickled jalapenos with a little juice. (If using tomatillos, blend in with jalapenos and cilantro).
Add the cilantro jalapeno puree to the mayo mixture. Stir in the buttermilk until you reach the desired consistency. Add fresh lime juice, if using.
Refrigerate until you're ready to serve.