Preheat the oven to 350°F (180°C) and line two baking trays with parchment paper. Slice the tops off 3 to 4 small edible white pumpkins to make lids. Scoop out the seeds and stringy fibers, brush the insides with about 1 tablespoon olive oil, and place on one tray.
Halve the butternut squash and remove the seeds. Leave the skin on for roasting.
Arrange the squash cut-side up with the onion, carrots, bell peppers, halved garlic head, and cherry tomatoes on the other tray. Drizzle with the remaining olive oil, season with salt, pepper, and optional curry powder, and add rosemary and thyme.
Roast the vegetables at 350°F (180°C) for about 30 to 40 minutes, until lightly caramelized and the squash is fork-tender. Turn peppers or carrots if needed. Roast the mini pumpkins for about 30 to 60 minutes, depending on size, until tender but sturdy enough to serve as bowls.
Let the vegetables cool slightly. Scoop the squash from its skin, squeeze the roasted garlic cloves from their skins, and discard inedible skins and woody herb stems. Transfer the roasted vegetables to a blender or deep pot.
Add 1 cup (240 ml) vegetable broth to the roasted vegetables. Reserve up to 1 more cup (240 ml) to adjust the consistency.
Blend carefully until smooth, adding the reserved broth gradually as needed. Stir in cream if using, taste, and adjust salt and pepper. Reheat gently if necessary.
Place each warm mini pumpkin on a plate and ladle in the hot soup.
Garnish with toasted pumpkin seeds, crumbled goat cheese if desired, and fresh basil. Serve right away.