Preheat your oven to 200°C (390°F). Arrange the chopped sweet potatoes and carrots on a baking sheet, drizzle with olive oil, and sprinkle with salt and pepper. Toss to coat evenly, then spread out in a single layer. Roast for 25-30 minutes, until tender and caramelized around the edges, filling the kitchen with a warm, sweet aroma.
Meanwhile, heat a large pot over medium heat. Add a splash of oil and sauté the chopped onion until translucent and slightly golden, about 5 minutes. The onion should emit a gentle sizzling sound and turn a soft, clear color.
Add the grated fresh ginger to the onion and cook for another minute, until fragrant. The mixture will release a lemony aroma and the ginger will turn a little darker at the edges.
Once the roasted vegetables are ready and cool enough to handle, add them to the pot with the sautéed onion and ginger. Pour in the vegetable broth and stir to combine. Bring the mixture to a gentle simmer, allowing the flavors to meld for about 10 minutes.
Using an immersion blender, blend the soup directly in the pot until smooth and velvety. Alternatively, carefully transfer the hot mixture to a blender and puree in batches, then return to the pot. The soup should be thick, creamy, and free of lumps.
Stir in the coconut milk for added creaminess and a subtle tropical flavor. Taste and season with salt and pepper as needed. Let the soup simmer for a few more minutes to incorporate the flavors.
Remove the soup from heat, and let it sit for a couple of minutes. Serve hot, garnished with a drizzle of coconut milk or fresh herbs if desired. Enjoy the cozy, silky bowl of roasted sweet potato and carrot soup!