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1
Preheat the oven to 425F.
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2
Use a fork or sharp knife to prick the sweet potatoes in several places.
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3
Place on a piece of aluminum foil and bake until the sweet potatoes are tender and can be easily squeezed, 60 to 75 minutes.
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4
(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.
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5
Bake until the potatoes are tender, 30 to 45 minutes.)
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6
Pour the oil into a 3-quart saucepan over medium heat.
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7
When it starts to shimmer, add the carrots, celery, leek, thyme, and a pinch of salt.
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8
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.
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9
(Take care not to allow the vegetables to burn.)
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10
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.
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11
The mixture will be chunky.
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12
Stir in the stock and combine well.
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13
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.
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14
Allow the mixture to cool slightly, then remove and discard the thyme.
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15
Use a handheld immersion blender to puree the soup base, which will be very thick.
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16
(Alternatively, you can puree it in a blender or food processor.
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17
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.)
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18
Taste and add salt if needed.
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19
Let the soup base cool to room temperature.
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20
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.
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21
It will keep frozen for several months.
