Preheat your oven to 200°C (390°F) and line a large baking sheet with parchment paper.
Peel and seed the butternut squash, then cut it into 2-inch chunks. Toss these with a tablespoon of olive oil, a pinch of salt, and pepper. Spread them evenly on the prepared baking sheet.
Peel the carrots and cut them into similar-sized pieces. Toss with a little olive oil and a pinch of salt, then add to the baking sheet alongside the squash.
Roast the vegetables for 40-45 minutes, flipping halfway through, until they are golden and tender, releasing that sweet, smoky aroma.
While the vegetables are roasting, peel and mince the garlic, then grate the fresh ginger. Set aside for later.
Once roasted, let the vegetables cool slightly until manageable. Transfer them to a large pot.
Pour in the vegetable broth and bring the mixture to a gentle simmer. Cook for about 10 minutes to let the flavors meld.
Use an immersion blender directly in the pot, or transfer the soup in batches to a blender. Blend until smooth and velvety, adjusting the consistency with more broth if needed.
Stir in the juice of a lemon to brighten the flavors. Taste and adjust salt if necessary.
Serve the soup hot, optionally topped with a swirl of crème fraîche or toasted seeds for extra texture and flavor.