1. Add the mayonnaise, buttermilk, sour cream, salt and garlic powder to a bowl and thoroughly mix together, preferably with a whisk.
2. Cut the blue cheese from the wedge and crumble it up to be added to the dressing. This is much better if you buy a wedge of blue cheese and crumble it up yourself rather than buying the pre-crumbled pieces in a plastic container.
3. Add the blue cheese and mix it in well until it is evenly incorporated.
4. Refrigerate it for at least 1/2 hour before using.