Spray a slow cooker with olive oil and add the cubed potatoes with the chicken broth and garlic. Place the bundle of herbs on top. It will infuse subtle savory flavor into the potatoes. Cook 3.5 hours on high.
Heat the butter, milk, and cheese in a saucepan, frequently stirring until smooth. Remove the mixture from the heat and stir in the yogurt (or sour cream). Season with salt and pepper.
Pour the cheese mixture into the slow cooker over the potatoes. Using a potato masher or handheld blender, whip the potatoes until you achieve your desired consistency.