In a small bowl, mix the sour cream and mayonnaise.
Mix in the salt, pepper, and garlic powder.
Add the blue cheese crumbles and mix them in thoroughly. Press on them to help extract their flavor into the dip.
If you'd like to thin the dip out and use it as a salad dressing, stir in 1-2 tablespoons of water. Serve immediately.
Video
Notes
For a thick and creamy dressing, use full-fat versions of the ingredients. If the sour cream has liquid on top, carefully pour it out before using.
You can keep this dressing in an airtight container in the fridge for up to five days. Give it another stir before serving, and add a bit more water if it has thickened too much while stored. I don't recommend freezing this dressing.