Using a fork, combine all the ingredients in a bowl. If you want to keep some blue cheese crumbles, do not mash them too much.
Transfer the dressing into a lidded jar or an airtight container and refrigerate before serving. This dressing lasts in the fridge as long as the yogurt you use does, so check the expiration date in the pack before throwing it out.
Notes
If you prefer a milder blue cheese flavor, add a little more yogurt or a little bit of milk.