Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a medium bowl, whisk together the flour, baking soda, and salt.

In a large bowl, beat the softened butter, peanut butter, granulated sugar, and brown sugar until creamy.

Add the egg and vanilla extract, mixing until well combined.

Gradually add the flour mixture to the wet ingredients, mixing until just combined.

Fold in the mini chocolate chips and crushed graham crackers.

Scoop tablespoon-sized portions of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Use your finger to create a small indentation in the center of each cookie.

Place a few mini marshmallows in the indentation of each cookie.

Bake for 10-12 minutes, or until the edges are lightly golden.

Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.

Once cooled, spread a layer of peanut butter on the bottom of one cookie and sandwich it with another cookie, marshmallow side down.

Repeat with the remaining cookies.