Preheat your oven to 200°C (390°F). Line a baking sheet with parchment paper, and trim the tops of the carrots. Toss them with 2 tablespoons of olive oil, a pinch of salt, and pepper. Spread evenly on the baking sheet.
Roast the carrots in the oven for 25-30 minutes until they are deeply golden and caramelized at the edges, shaking the pan halfway through for even cooking.
While the carrots roast, heat 1 tablespoon of olive oil in a large pot over medium heat. Add the diced onion and minced garlic, sautéing gently for about 5-7 minutes until fragrant and translucent, with a slight golden hue.
Once the carrots are roasted and slightly cooled, peel them if you prefer a smoother soup, then chop into smaller pieces. Add the roasted carrots to the pot with the sautéed aromatics.
Pour in the vegetable stock and bring the mixture to a gentle simmer over medium heat. Add the rinsed red lentils and stir well.
Cook for about 15-20 minutes, stirring occasionally, until the lentils have broken down and the soup is thick and velvety. Adjust the heat to prevent sticking or boiling over.
Use an immersion blender directly in the pot to blend the soup until smooth and creamy, or carefully transfer it to a blender in batches. Blend until the texture is silky and even.
Stir in the remaining 1 tablespoon of olive oil, a squeeze of lemon juice, and season with salt, pepper, and cumin if using. Taste and adjust the seasoning as needed.
Let the soup sit for a minute or two to allow flavors to meld. Then, ladle into bowls and garnish with fresh herbs or a drizzle of olive oil if desired. Serve hot and enjoy the comforting, richly flavored soup.
