In a medium bowl, stir together the sour cream, mayonnaise, and buttermilk. Add the garlic powder and onion powder and stir well. Season to taste with salt.
Fold in the crumbled blue cheese. Cover and refrigerate until serving.
Crack some black pepper over the top just before serving.
Notes
Texture and flavor--If you want the dressing to be runnier, thin with a little milk or buttermilk until you reach your desired consistency. If you prefer a tangier dressing, add a couple drops of lemon juice.
Storage--Store leftover dip in a sealed container in the fridge for up to 5 days. If the dip begins to separate, give it a stir before serving.
Dietary--This recipe is suitable for gluten-free diets.