01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - In a medium bowl, whisk together the flour, baking soda, salt, cinnamon, and nutmeg until well combined. Set aside.
03 - In a large bowl, whisk together the melted butter, light brown sugar, and granulated sugar until the mixture is smooth.
04 - Add pumpkin purée, egg yolk, and vanilla extract to the wet mixture; whisk until fully blended.
05 - Gradually fold dry ingredients into the wet mixture until just combined; do not overmix.
06 - Gently fold in chocolate chips, mini marshmallows, and graham cracker pieces until evenly distributed.
07 - Scoop heaping tablespoons of dough onto prepared sheets, spacing about 2 inches apart.
08 - Bake for 11 to 13 minutes, or until edges are set and tops appear slightly underbaked.
09 - Let cookies cool on baking sheets for 5 minutes. Transfer to a wire rack to cool completely.