teaspoons plus 2 tablespoons extra-virgin olive oil
pounds sweet potatoes (about 3 medium), peeled and cut into 1/2-inch cubes
medium yellow onion, peeled and diced
teaspoon cumin seeds
cups low-sodium vegetable stock
teaspoon freshly ground black pepper
teaspoon ground turmeric
Fine sea salt
- Heat oven to 400 degrees. Remove some of the excess paper from the garlic bulb, leaving the bulb intact. Rub the bulb with 2 teaspoons oil and place it in the center of a rimmed baking sheet.
- In a large bowl, toss the sweet potatoes, onion and cumin seeds with the remaining 2 tablespoons olive oil. Spread them in a single layer on the baking sheet and roast until the sweet potatoes are slightly caramelized and tender and the garlic has softened, about 25 minutes. Remove from the oven and let rest until the vegetables are cool enough to handle, about 8 minutes.
- While the vegetables roast, prepare the infused oil: In a small saucepan over medium, heat the neutral oil, taking care not to burn it. (Measure the oil’s temperature with a thermometer; it should read about 325 degrees. You could also test the temperature with a Sichuan peppercorn: It should sizzle when tossed in.)
- Once the oil is hot, remove it from the heat, add the red-pepper flakes, garlic and Sichuan peppercorns. Cover with a lid and let steep for at least 20 minutes. (The oil can be prepared a day ahead of time and stored in an airtight container in the refrigerator for up to 1 week.)
- Transfer the cooked sweet potato mixture to a blender. Squeeze the softened garlic pulp out of the pods and add the pulp to the blender. Add 1/4 cup stock to the baking sheet to help wash off any stuck bits and transfer the liquid and bits to the blender. Add the remaining stock, the black pepper and turmeric to the blender and purée on high speed until smooth and creamy. Taste and add salt as needed. Transfer the soup to a medium saucepan and rewarm over low as needed.
- Divide the soup among bowls and drizzle with a generous tablespoon or two of the infused oil, stirring the oil beforehand so the settled bits show up in every tablespoon. Serve immediately.