Preheat the oven to 400°F (200°C). Toss sweet potatoes and carrots with a tablespoon of olive oil and spread them evenly on a baking sheet. Roast for about 25-30 minutes until tender and slightly caramelized, filling the kitchen with a sweet, roasted aroma.
Meanwhile, toast cumin seeds in a dry skillet over medium heat for 1-2 minutes until fragrant and slightly darker; then grind them into a fine powder using a mortar and pestle or spice grinder.
In a large pot, heat the remaining olive oil over medium heat. Add the minced ginger and toasted cumin powder, sautéing for about 1 minute until fragrant and aromatic.
Add the roasted sweet potatoes and carrots into the pot, stirring to coat them with the spices and aromatics. Let them cook together for a couple of minutes.
Pour in the vegetable broth and bring the mixture to a simmer. Reduce the heat to low, cover, and cook for an additional 10 minutes to meld the flavors.
Use an immersion blender or transfer the soup carefully to a blender and blend until smooth and velvety, about 1-2 minutes. Resturn to the pot if using a regular blender.
Taste the soup and season with salt and pepper as desired, adjusting the seasoning to your preference for a balanced, warm flavor.
Reheat gently if needed, then ladle the hot soup into bowls, serving immediately while steaming and fragrant with a smooth, thick texture.
