Preheat the oven to 400F.

Cut the carrots in half, then halve them lengthwise. Put them in a large bowl, along with 3 tablespoons of extra virgin olive oil, the thyme, salt and pepper. Toss to coat the carrots. Transfer them to a baking sheet and roast in the oven until they begin to brown, 45 to 50 minutes, turning half way through the cook time. Remove from oven.

In a large saucepan, heat the remaining 3 tablespoons of olive oil. Add the leek and saute until aromatic, 3 to 5 minutes. Add the ginger and red pepper flakes, stir to combine, and cook for an additional minute.

Add in the roasted carrots and vegetable broth. Bring to a simmer over medium heat; let simmer for 8-10 minutes. Turn the heat to low, cover, and simmer an additional 20 minutes. Remove from heat and let come to lukewarm.

Working in small batches, transfer the mixture into a blender or food processor and process until smooth. Return the mixture to the pot and bring back to the desired serving temperature. Add the lime zest and juice and season to taste with salt and pepper. Serve with sour cream, if desired.