Whisk the flour, baking soda, and salt together in a medium bowl. Set aside.

In a separate bowl, beat together the butter and granulated sugar until smooth, about 1 minute. Then, add the brown sugar and beat until creamy, about 30 seconds.

Add the egg and vanilla and beat until combined. Add the dry ingredients to the wet ingredients, and mix on low until combined and no streaks of flour remain.

Stir in the chocolate chips.

Using a 1-tablespoon measure, scoop out 6 balls of dough. Press a marshmallow chunk on top of one dough ball.

Place another one-tablespoon-sized dough ball on top of each marshmallow. Use your fingers to seal the edges together as best as you can, and then roll the cookie dough ball so that the marshmallow is completely hidden inside the dough ball. Repeat with the rest of the dough, making 12 cookies total.

Place the cookies on a plate (or keep on the baking sheet if it fits). Then, break 3 graham cracker sheets into 12 pieces each (break into the four quadrants following the lines on the cracker and then each quadrant into 3 smaller pieces). We’re putting 3 small pieces of graham cracker in each cookie, so we need 36 pieces of graham cracker from 3 whole sheets. Each quadrant of a graham cracker makes 3 pieces for one cookie. Three sheets = enough pieces for all 12 cookies. (The remaining graham cracker sheet will be crushed and sprinkled over the cookies after baking). Press three small pieces of graham cracker into each dough ball.

Refrigerate the cookie dough balls for 30 minutes while you preheat the oven to 350°F.

Space 6 cookie dough balls evenly on a large baking sheet, and add a few extra chips on top of each cookie. Bake for 11–13 minutes, until the cookies are starting to turn golden brown around the edges.

Right when the cookies come out of the oven, use your fingers to crush the remaining graham cracker sheet and sprinkle it over the cookies while still warm. Then, let the cookies cool completely on the cookie sheet (so that the marshmallow doesn’t stick to the pan!).