Preheat the oven to 350°F (175°C). In a mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.

Add the pumpkin puree, egg, and vanilla extract to the mixture and mix until well combined.

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.

Scoop tablespoon-sized amounts of dough onto a baking sheet lined with parchment paper, spacing them about 2 inches apart.

Press a few chocolate chips and mini marshmallows into the center of each cookie dough ball.

Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden. Let cool on the baking sheet for a few minutes before transferring to a wire rack.