- 2 (10- to 12-ounce) sweet potatoes
- 2 tablespoons extra virgin olive oil
- 2 carrots, peeled and thinly sliced
- 1 celery stalk, thinly sliced
- 1 small leek, white and pale greens, thinly sliced
- 2 sprigs thyme
- Kosher or sea salt
- Pinch of curry powder
- 2 cups light chicken or vegetable stock, warmed
- Preheat the oven to 425°F.
- Use a fork or sharp knife to prick the sweet potatoes in several places. Place on a piece of aluminum foil and bake until the sweet potatoes are tender and can be easily squeezed, 60 to 75 minutes. (Alternatively, to speed up the process, microwave the pricked sweet potatoes on High for 1 minute, then carefully transfer to the oven on a piece of foil. Bake until the potatoes are tender, 30 to 45 minutes.)
- Pour the oil into a 3-quart saucepan over medium heat. When it starts to shimmer, add the carrots, celery, leek, thyme, and a pinch of salt. Stir to combine well, then decrease the heat to low, cover the pot, and allow the vegetables to sweat in their own juices until very soft, 10 to 15 minutes. (Take care not to allow the vegetables to burn.)
- Scrape into the saucepan the soft flesh from the roasted sweet potatoes, add the curry powder, and stir to combine, mashing the sweet potato flesh with a spoon. The mixture will be chunky. Stir in the stock and combine well. Bring the mixture to a boil, then decrease the heat so the mixture gently simmers, and cook, covered but with the lid slightly ajar, for about 15 minutes to let the flavors meld. Allow the mixture to cool slightly, then remove and discard the thyme.
- Use a handheld immersion blender to puree the soup base, which will be very thick. (Alternatively, you can puree it in a blender or food processor. If using a blender, be sure to remove the center cap on the lid and cover with a dish towel to let steam escape, and work in small batches to avoid splattering the soup.) Taste and add salt if needed.
- Let the soup base cool to room temperature. Divide it into 4 portions and use immediately, refrigerate for up to 2 weeks, or freeze in small containers or heavy-duty freezer-safe resealable plastic bags, pressing as much air out of the bag as possible before sealing. It will keep frozen for several months.