Preheat your oven to 400°F (200°C). Line a large rimmed baking sheet with parchment paper or aluminum foil for easy cleanup. Carefully cut each acorn squash in half from stem to point. Use a sturdy spoon to scoop out the seeds and stringy pulp from the center of each half.
In a small bowl, whisk together the melted butter, pure maple syrup, ground cinnamon, nutmeg, salt, and black pepper. Stir until the mixture is well combined and the spices are evenly distributed throughout the liquid.
Place the squash halves on the prepared baking sheet, cut side up. Brush the maple butter mixture generously over the flesh and the rim of each squash half. If you have extra glaze, pour a little bit into the hollowed-out centers.
Place the baking sheet in the center of the oven. Roast for 35 to 45 minutes, or until the squash is tender when pierced with a fork and the edges are golden brown. About halfway through, you can use a brush to baste the squash with the juices that have pooled in the center.
Remove the squash from the oven and let them rest for 5 minutes. Use a spoon to drizzle any remaining glaze from the center back over the edges before serving warm.