Preheat your oven to 400°F (200°C). Toss the sweet potato cubes and sliced carrots with olive oil, cumin, and a pinch of salt and pepper. Spread them evenly on a baking sheet and roast for about 25-30 minutes, until they are caramelized and tender, and fragrant with toasty spices.
While the vegetables roast, peel and mince the garlic cloves. Prepare your vegetable broth and keep it warm on the stove or microwave for easy blending later.
Once the vegetables are done roasting, transfer them to a large pot. Add the minced garlic and cook over medium heat for a minute, until the garlic is fragrant but not browned, filling your kitchen with a warm aroma.
Pour the hot vegetable broth into the pot with the roasted vegetables. Bring everything to a gentle simmer and cook for about 5 minutes to let the flavors meld.
Use an immersion blender to blend the soup directly in the pot until smooth and velvety, or transfer carefully to a blender and purée in batches. Taste and adjust seasoning with salt and pepper, adding a splash of lemon juice if desired for brightness.
Return the blended soup to a gentle simmer if needed, just to warm through. Check the consistency and add a little more broth if it’s too thick, blending again for a silky texture.
Serve hot, garnished with a drizzle of olive oil, a sprinkle of fresh herbs, or a dollop of yogurt if desired. Enjoy the rich, earthy sweetness and smooth texture of this comforting roasted vegetable soup.