Preheat oven to 425 degrees F. To make the dressing: whisk together sour cream, mayo, buttermilk, salt, pepper and vinegar. Gently fold in blue cheese crumbles. Place in an airtight container (I like using mason jars for dressing) and refrigerate until ready to use.
Add potatoes to a large bowl. Drizzle with olive oil and toss to coat. Sprinkle with salt, pepper and garlic powder. Toss again.
Tear off two pieces of foil about 16 inches each. Add half the potatoes to each piece of foil then wrap up tightly. Place the foil packets on a baking sheet then place in the oven. Cook for 45 minutes, flipping halfway through cooking time.
Remove from oven and very carefully open the foil packets. Drizzle each with the blue cheese dressing.