Peel and chop potatoes, place in medium pot with veg broth. Boil until very tender, covered. Meanwhile, dice and saute onion with butter until translucent. Transfer to blender and add in milk and beans with liquid, nutritional yeast and some seasoning. Puree until very smooth.
When potatoes are tender, mash them into the broth with a potato masher. Add in the blender mix and stir, heating through. Taste and adjust seasoning as needed. Garnish with chives.