Be careful not to let this soup boil when reheating—you want to retain the delicate properties of the miso, which can be destroyed by high heat.
- 1 small sweet potato
- 1 3×5-inch piece kombu
- ¾ ounce bonito flakes (about 1½ packed cups)
- 1 5.5-ounce can unsweetened coconut milk
- ¼ cup white miso
- 1 tablespoon finely grated fresh turmeric or 1 teaspoon ground turmeric
- 1 tablespoon fresh lime juice
- Toasted coconut flakes, crushed salted, roasted peanuts, and chili oil (for serving)
- Preheat oven to 450°. Pierce potato several times with a fork or sharp knife. Roast potato on a rimmed baking sheet until tender, 35–45 minutes. Let cool, then scoop out flesh; discard skin.
- Meanwhile, combine kombu and 4 cups water in a large pot. Let sit until kombu softens, 25–30 minutes. Bring to a simmer over medium heat. Immediately remove from heat once water starts simmering; fish out kombu and discard. Add bonito flakes and stir once to submerge them. Return to a gentle boil, reduce heat, and simmer about 5 minutes. Remove from heat and let steep 15 minutes (this ensures you get the most flavorful broth, or dashi, possible). Strain dashi through a fine-mesh strainer into a medium bowl. Discard solids; wipe out pot.
- Transfer dashi to a blender. Add sweet potato, coconut milk, miso, and turmeric. Blend until smooth. Return to pot and bring to a very gentle simmer. Remove from heat and stir in lime juice.
- Divide soup among bowls. Top with coconut flakes and peanuts, then drizzle with chili oil.