Add the mayonnaise, sour cream, avocado, and diced jalapeno to a blender or food processor. Blend until smooth. 

Move this mixture to a large bowl.

Add chopped dill, chopped chives, garlic powder, onion powder, MSG (if using) and salt and pepper to the large bowl with the mayonnaise mixture and whisk everything well to combine. 

Taste now to see if you think it needs more salt and pepper. I typically go heavy on the pepper. 

If you think the sauce is too thick at this point you can add buttermilk or regular milk a tablespoon at a time until you get the consistency you want. I usually only need about 3 tablespoons to hit a thick dressing stage but if you're making this for salads, you might want to add more. If you want a dip for chips or French fries, you don't need to add any extra liquid at all.

Store in a jar or container with a lid in the refrigerator for no more than 2 weeks.