Add the mayonnaise, sour cream, chopped dill, chopped chives, garlic powder, onion powder, MSG (if using) and salt and pepper to a medium-sized bowl. Whisk well to combine.
Taste now to see if you think it needs more salt and pepper. I typically go heavy on the pepper.
You can stop now (without the buttermilk) if you want more of a mayonnaise like consistency to spread on sandwiches.
Add buttermilk a little bit at a time and whisk until you reach the right consistency. 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.
Store in a jar or container with a lid in the refrigerator for no more than 2 weeks.
Notes:
If you want this to be more of a spread like mayonnaise, you can omit the buttermilk entirely. This is great Ranch that you can use for a dip for chips, use it on a salad or if you live in the Midwest, you can put it on anything.