PREHEAT oven to 425F. Toss carrots and sweet potatoes with 1 tbsp oil on a baking sheet. Roast until tender, 20 min.
HEAT remaining 2 tbsp oil in a large pot over medium. Add onion, leek and garlic and cook, stirring occasionally, until tender, about 10 min. Stir in curry paste and fish sauce. Cook for 1 min.
ADD roasted vegetables, all but ¼ cup coconut milk and broth. Boil, then reduce heat to medium-low and simmer, uncovered, for 10 min. Remove from heat.
PURÉE soup until smooth, using an immersion blender. Return pot to heat, reduced to low, and stir in lime juice and salt. Ladle into bowls and top with remaining ¼ cup coconut milk, peanuts, cilantro and coconut.
