Preheat the oven to 425°F and line a baking sheet with parchment paper. Carefully halve the butternut squash lengthwise and scoop out the seeds. Brush the cut sides with 1 tablespoon olive oil and season lightly with salt and pepper.
Place the squash cut-side down on the baking sheet and roast for 40–50 minutes, until the flesh is completely tender and lightly caramelized. Let it cool for about 10 minutes before handling.
While the squash roasts, heat the remaining olive oil in a large soup pot over medium heat. Add the shallot and a pinch of salt and cook for 3–4 minutes until softened and lightly golden. Stir in the garlic and cook for another minute.
Scoop the roasted squash flesh away from the skin and add it to the pot with the sautéed aromatics. Pour in the vegetable broth, then add the maple syrup, nutmeg, black pepper, and remaining salt.
Bring the mixture to a gentle simmer and cook for 10–15 minutes, stirring occasionally. This gives the roasted squash and aromatics time to meld with the broth.
Carefully blend the soup with an immersion blender until completely smooth, or blend in batches using a countertop blender. Stir in the butter and lemon juice, then add a little more broth if you prefer a thinner consistency.
Taste and adjust the salt, pepper, or maple syrup as needed. Ladle the hot soup into bowls and garnish with toasted pumpkin seeds and fresh parsley before serving.
