Preheat oven – Heat oven to 400°F (200°C). Line a baking sheet with parchment paper.
Prepare squash – Cut butternut squash in half lengthwise. Scoop out seeds. Place cut side down on baking sheet.
Roast – Roast for 30–35 minutes until flesh is tender and easily pierced with a fork.
Scoop & mash – Scoop flesh into a bowl. Add butter, salt, pepper, and optional cinnamon/nutmeg. Mash with a potato masher or puree with an immersion blender for extra creaminess.
Serve – Transfer to a serving dish. Garnish with fresh herbs and toasted pepitas.