In a high speed blender or NutriBullet, add the cashews with 1 cup water. Blend on high until smooth then set aside.In a large pot, warm butter over medium heat. Add the onion, celery, carrot, and garlic. Sprinkle with salt and cook for about 3 minutes, until fragrant.Sprinkle chickpea flour on top of vegetables and stir to combine. Cook for about 1 minute. Pour in 2 cups vegetable broth, a little bit at time, stirring between each addition until smooth. The mixture will be thick in the beginning then thin out as you continue to add the broth. To the pot, add the potatoes and the cashew milk. Cover and simmer for about 30 minutes, stirring intermittently. The soup will continue to thicken as it cooks. Add more broth, as needed, until desired consistency is reached.Once potatoes are tender (you can check by piercing with a fork), serve soup warm topped with chopped chives and shiitake bacon, and enjoy!