01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together flour, baking soda, salt, cinnamon, and nutmeg until evenly blended.
03 - In a large bowl, whisk together melted butter, brown sugar, and granulated sugar until smooth.
04 - Add pumpkin purée, egg yolk, and vanilla extract to the sugar mixture. Whisk until fully combined.
05 - Gradually fold the dry ingredients into the wet mixture using a spatula just until incorporated. Avoid overmixing.
06 - Gently fold chocolate chips, mini marshmallows, and graham cracker pieces into the dough.
07 - Scoop heaping tablespoons of dough onto the prepared baking sheets, spacing each portion about 2 inches apart.
08 - Bake for 11 to 13 minutes until edges are set and tops appear slightly underbaked.
09 - Allow cookies to cool on baking sheets for 5 minutes. Transfer to a wire rack to cool completely.