Preheat oven to 375 degrees F, line a large, rimmed baking sheet with foil or parchment paper, and set aside.

In a medium bowl, whisk together the flour, baking soda, salt and cinnamon, then set aside.

In the bowl of a stand mixer (or a large bowl if using a hand mixer,) cream together the softened butter and sugars, using the paddle attachment, until fluffy, about 2-3 minutes.

Mix in the vanilla and then add the eggs, one at a time, beating well after each addition.

Gradually mix in the flour mixture, incorporating well after each addition.

Lay out the graham crackers on the prepared baking sheet leaving no gaps between them.

Use an medium cookie scoop and place balls of cookie dough on the graham crackers. I did about 5 scoops in each row with a little space in between. Use the back of the cookie scoop to gently press down on the dough to spread it out. There will be some gaps, but the dough will spread as it cooks so don't worry about that.

Bake for 5 minutes, then remove and press press Hershey pieces and 1/4 cup marshmallows sporadically on top. You can also gently press/spread the dough if you don't feel it's spread enough to the edges at this time. Bake for 5-7 more minutes, until the cookie dough is just set.

Cool completely in the pan. If you need to cut them before they are fully cooled and you don't want the melty chocolate smears (but...that's half the fun!), you can stick them in the fridge for a bit, after they've cooled on their own for at least 10 minutes.

Cut through the cookie layer into squares, where the graham crackers are already separated. I use the foil edges that overhang on the baking sheet to gently remove the bars from the pan before cutting, as you can easily see where the graham cracker breaks are this way, which makes for easier cutting.