Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the creamy peanut butter and softened butter. Beat with an electric mixer until smooth and creamy.
Add the brown sugar and granulated sugar to the bowl, and continue to mix until well combined.
Beat in the egg and vanilla extract until fully incorporated.
In a separate bowl, whisk together the flour, baking soda, and salt. Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Fold in the mini marshmallows, chocolate chips, and graham cracker crumbs until evenly distributed.
Using a cookie scoop or tablespoon, drop rounded balls of dough onto the prepared baking sheet, spacing them about 2 inches apart.
Bake in the preheated oven for 10-12 minutes, or until the edges are lightly golden.
Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Once cooled, pair the cookies together to form sandwiches, with the marshmallows and chocolate chips in the middle.