place half of the blue cheese in the jar of a blender

add the buttermilk, sour cream, mayonnaise and vinegar

put the top on the blender jar-sure you're thinking I'm silly to tell you this but it's from experience

blend until smooth

pour out the dressing scraping out all the last bits

gently stir in the last of the blue cheese

taste for salt and pepper add as needed

store in jar in the refrigerator until ready to use

If you prefer you can add ALL the blue cheese to the blender and make a super smooth dressing but I really prefer it with big chunks of cheese.