Preheat your oven to 200°C (390°F). Spread the chopped sweet potatoes and carrots on a baking sheet, drizzle with olive oil, and toss to coat evenly. Roast for 30-35 minutes until caramelized and tender, filling the kitchen with a sweet, smoky aroma.
Meanwhile, heat a tablespoon of olive oil in a large pot over medium heat. Add the chopped onion and cook, stirring occasionally, until fragrant and translucent, about 5 minutes. The onion should soften and become slightly golden.
Add the minced garlic to the pot and cook for another minute until fragrant, being careful not to burn it. The garlic should release a rich aroma, blending with the onion base.
Once the roasted vegetables are ready, transfer them to the pot with the sautéed onions and garlic. Pour in the vegetable broth and bring the mixture to a gentle simmer. Let it cook for about 10 minutes, allowing the flavors to meld.
Use an immersion blender to carefully blend the soup directly in the pot until smooth and velvety. If you prefer, transfer the mixture in batches to a regular blender, blending until silky, then return to the pot.
Stir in lemon juice, then season with salt and pepper to taste. Adjust the seasoning as needed, tasting for balance and brightness.
Serve the soup hot, garnished with a swirl of cream or a sprinkle of fresh herbs if desired. Enjoy its rich, smoky sweetness and comforting warmth in every spoonful.