In a large pot, heat 1 tbsp oil over medium heat. When the pot is hot, add onions and carrots. Season with salt and black pepper. Cook for 4-6 min, stirring occasionally, until almost tender.
1 tbsp oil, 1 small onion, chopped, 1 carrot, peeled and diced
Add garlic and ginger and cook for another 1 min, stirring constantly, until fragrant.
3 cloves garlic, minced, 1 inch piece ginger, minced or grated
Add tomato paste, curry powder, cumin, coriander, turmeric and cayenne or chili flakes, if using. Cook for 1 min, stirring constantly, to toast spices.
2 tbsp tomato paste, 2 tsp mild curry powder, 1 tsp ground cumin, ½ tsp ground coriander, ½ tsp ground turmeric, ½ tsp ground cayenne pepper or red pepper flakes
Add sweet potatoes, lentils, coconut milk and vegetable stock. Season with salt. Bring to a simmer over high, stirring and scraping up all the bits from the bottom of the pot. Once simmering, reduce heat to medium-low. Cook for 20-24 min, stirring occasionally, until sweet potatoes and lentils are tender.
4 cups sweet potato, cut into ½-inch cubes, 1 cup dried red lentils, rinsed, 1 can coconut milk, 4 cups vegetable broth
Using an immersion blender or by transferring half the soup to a blender, blend about half of the soup. Blending only half the soup gives it the perfect texture. Add the blended portion back to the pot if you used a blender and stir to combine.
To adjust the thickness to your preference, stir in 1-2 cups of water (optional). I usually use a full 2 cups but it depends how thick you like it. Note that it will thicken after storing and can also be adjusted with liquid when you reheat it. Stir in the lime juice and season with salt to taste.
½ lime
Divide soup between bowls. Sprinkle fresh cilantro over top. Serve lime wedges alongside. Sprinkle with red chili flakes if you want a little extra spice.