Preheat the oven to 375°F. Line baking sheets with parchment paper.
In a large mixing bowl, whisk together the flour, baking soda, salt, and graham cracker crumbs. Set aside.
In a separate large mixing bowl, beat the softened butter, granulated sugar, and brown sugar until light and creamy. Beat in the eggs and vanilla extract until fully incorporated.
Gradually add the dry ingredients to the butter mixture, mixing just until combined. Fold in the chocolate chips.
Reserve about ¼ cup of the mini marshmallows and half of one chopped chocolate bar for topping the baked cookies. Fold the remaining marshmallows, the remaining chopped chocolate, and any larger graham cracker pieces into the dough.
Scoop the dough into 1½ tablespoon portions and place them about 2 inches apart on the prepared baking sheets.
Bake for 8 to 10 minutes, or until the edges are lightly golden and the centers are just set. Bake in batches if needed.
Let the cookies cool on the baking sheets for 2 to 3 minutes. While they are still warm, gently press the reserved marshmallows and chopped chocolate into the tops of the cookies.
Transfer the cookies to a cooling rack and cool completely before serving.
Christina's Notes
Use a combination of chocolate chips and chopped milk chocolate bars for the best texture. The chips help the cookies hold their shape, while the chocolate bars create gooey pockets of melted chocolate.
Tear larger mini marshmallows in half before mixing them into the dough so they distribute more evenly.
For extra flavor, lightly toast a few of the marshmallows with a kitchen torch before pressing them onto the warm cookies.
Use a round cookie cutter to gently swirl the cookies immediately after baking if you'd like perfectly round cookies.
If the chocolate becomes too soft while the cookies cool, place the cooling rack in the refrigerator for 10 to 15 minutes to help the chocolate set.
Store the cookies in an airtight container at room temperature for up to 4 days.
Freeze baked cookies in a freezer-safe container for up to 3 months. Thaw at room temperature before serving.
Cookie dough can be scooped and frozen for up to 3 months. Bake directly from frozen, adding 1 to 2 minutes to the baking time.