Preheat oven to 400°F (200°C). Cut the squash in half, scoop out the seeds, and roast cut-side down for 45-60 minutes, or until tender. Let cool, then scoop out the flesh and mash until smooth.
In a large bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Beat in the egg, maple syrup, and vanilla extract until well combined.
Stir in the butternut squash puree until evenly distributed.
In a separate bowl, whisk together the flour, baking soda, cinnamon, nutmeg, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Be careful not to overmix.
Stir in the rolled oats and any optional mix-ins like chocolate chips or nuts.
Cover the dough and refrigerate for at least 30 minutes. This helps prevent the cookies from spreading too much.
Preheat oven to 375°F (190°C). Drop rounded tablespoons of dough onto a baking sheet lined with parchment paper.
Bake for 10-12 minutes, or until the edges are golden brown and the centers are set.
Let the cookies cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.
