Using the large holes of a box grater, grate a few carrots to yield about ⅓ cup; set aside for garnish. Slice the remaining carrots into ¼-inch-thick coins.
In a large soup pot over medium heat, heat the oil until shimmering. Add the onion and cook, stirring occasionally, until softened, about 3 minutes. Add the garlic and ginger and cook, stirring, about 1 minute more. Stir in the sliced carrots, cashews, salt and pepper; add the broth and bring to a boil.
Reduce the heat to medium-low, cover and simmer until the carrots are tender, about 10 minutes. Remove the pot from the heat, and let cool slightly, about 10 minutes.
Meanwhile, in a small bowl, stir together the grated carrots, sesame seeds, ½ teaspoon of sesame oil, ½ teaspoon of honey, the rice vinegar and a pinch of salt.
Add the miso, and the remaining 1 tablespoon of honey and 1 ½ teaspoons of sesame oil to the soup, then use an immersion blender to puree it until smooth. Taste, and add more miso, if desired. (Alternatively, let the soup cool completely, then puree in batches in a regular blender and return to the stove to warm through over medium-low heat. If the soup seems too thick, add more broth, a splash at a time, until it reaches the desired consistency.)
Ladle the soup into bowls, garnish with the grated carrot mixture and serve hot.
