Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper or foil.
Slice the butternut squash in half lengthwise and scoop out the seeds using a spoon.
Rub the cut sides and inside the cavity of the squash halves evenly with olive oil.
Place the squash halves cut-side up on the prepared baking sheet.
In a small bowl, whisk together the melted butter, brown sugar, salt, and black pepper.
Spoon the butter and brown sugar mixture over the cut sides of the squash, letting it pool slightly in the seed cavities.
Bake for 45 to 55 minutes, or until the flesh is fork-tender and the edges are caramelized.
Allow to cool for 5 minutes before serving. Scoop the flesh out or serve cut into wedges.