Place all the ingredients in a mixing bowl and whisk to combine.
Store the dressing in an airtight container in the refrigerator.
Notes
Use Greek Yogurt: You can make the dressing with Greek yogurt in place of the sour cream.
Add other seasonings: The all purpose seasoning has a nice blend of flavors. However, you can add a little kick to your blue cheese dressing with a little hot sauce or red pepper flakes.
Variation tip: A dash of Worcestershire sauce for more umami flavor or use lemon juice from a bottle.
Extra Creamy: The recipe calls for several thick dairy ingredients. So add a little more buttermilk for extra tang.
Lighten: Swap the mayonnaise for light mayo and the sour cream for fat free versions.