Adapted from Genius Kitchen
Preheat oven to 350ºF. Grease a 9×13″ pan.
In a large bowl, beat butter and sugar together until well-combined. Add vanilla and egg and beat well. In a second bowl, combine the flour, crushed graham crackers, baking powder, and salt. Add the graham cracker mixture to the butter mixture and beat until blended (note that I used a hand mixer).
Transfer about 3/4 of the dough into the pan and smooth until the entire bottom of the pan is covered. The dough will be gooey so I thought it was easier to spread with my hands than a spoon. Bake for 15 minutes.
After removing the pan from the oven, evenly spread the chocolate chips to cover the baked layer. Do the same with the marshmallows. Take the remaining dough mixture and break it into pieces, sprinkling it over the marshmallows.
Bake for another 15-17 minutes (until top is slightly brown). Remove from oven and cool completely before cutting–otherwise they’ll break apart. If you want this served fresh/hot/warm, grab a spoon and dig in!