In a small bowl, place the blue cheese, mayo, sour cream, vinegar, lemon juice, dill, garlic powder, sugar, and several grinds of pepper. Stir to combine, breaking up the blue cheese crumbles as you mix. Season to taste, adding a pinch of salt if necessary.

If the dressing is too thick, add buttermilk, milk, or water, 1 teaspoon at a time, as needed to reach your desired consistency. Add less to create a thick, creamy dip and more to thin it to a drizzleable dressing.

Store leftover dressing in an airtight container in the refrigerator for up to 4 days. It will thicken in the fridge. Add milk or water as needed to thin before using.