Slice off and discard roots and dark-green tops of leeks. Cut leeks in half lengthwise. Fan out and rinse under cold water to remove any grit. Thinly slice. Melt butter in a large, wide saucepan over medium heat. Add leeks. Stir occasionally until very soft, 5 to 8 min.
Meanwhile, thinly slice carrots. Chop pear. When leeks are soft, stir in carrots, pear and curry paste. Pour in a little broth. Use a wooden spoon to scrape up and stir in any brown bits from pan bottom. Stir in remaining broth, salt and white pepper. Bring to a boil over high heat. Then reduce heat and simmer, uncovered and stirring occasionally, until carrots are very tender, 25 to 35 min.
Ladle one-third of soup into a food processor. Whirl until smooth, then pour into another saucepan or large bowl. Repeat with remaining soup. (Alternatively, use a hand blender.) Taste and add more salt and pepper if needed, as well as thyme, if using. Reheat, if necessary, then spoon into bowls. Top with a dollop of sour cream and a sprinkling of chives, if you wish. Soup will keep well, covered and refrigerated, up to 5 days, or freeze up to 2 months.
Nutrition (per serving)
Our luxurious fall soup gets its rich flavour from carrots, pears, leeks and curry.