In a medium-sized bowl, combine 1 cup of mayonnaise (like Hellmann's) and ½ cup of sour cream or Greek yogurt. Stir until they are well blended.
Pour in ½ cup of buttermilk and 1 tablespoon of extra virgin olive oil. Whisk everything together until the mixture is smooth and creamy.
Finely chop 1 tablespoon each of fresh chives, dill, and Italian parsley. If you don’t have fresh herbs, you can use 1 teaspoon of dried dill, chives, and parsley. Mash 1 small garlic into a paste and add it to the bowl.
Add ½ teaspoon each of granulated garlic and granulated onion. Then, stir in ¼ teaspoon of ground black pepper and ¼ teaspoon of cayenne for a bit of heat. If you like, you can also add ¼ teaspoon of sugar to balance the flavors, but this is optional.
Mix in 1 scant teaspoon of kosher salt. Then add 1 tablespoon of fresh lemon juice, white wine vinegar, or distilled vinegar. Adjust the acidity according to your taste by adding more or less vinegar or lemon juice.
Give the dressing a taste and adjust the seasoning if needed. You might want to add more salt, herbs, or acid to suit your preference.
For the best flavor, cover and refrigerate the dressing for at least an hour before serving. This allows the flavors to meld together.