Mix Dry Ingredients: In a medium bowl, whisk together the all-purpose flour, baking soda, salt, cinnamon, and nutmeg. Set aside.
Mix Wet Ingredients: In a large bowl, whisk together the melted butter, brown sugar, and granulated sugar until smooth. Add the pumpkin puree, maple syrup, vanilla extract, and egg yolk, and beat until fully combined.
Combine Wet and Dry Ingredients: Gradually stir the dry ingredients into the wet mixture until just combined. Be careful not to overmix.
Chill the Dough: Cover the dough with plastic wrap and refrigerate for at least 30 minutes. Chilling the dough helps the cookies keep their shape while baking.
Preheat the Oven: Preheat your oven to 350°F (175°C). Line baking sheets with parchment paper or a silicone baking mat.
Scoop and Shape the Dough: Use a cookie scoop or tablespoon to scoop out 1½ tablespoon-sized balls of dough. Place the dough balls on the prepared baking sheet, spacing them 2 inches apart.
Bake: Bake in the preheated oven for 10–12 minutes, or until the edges are set but the centers are still slightly soft.
Cool: Let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.