Preheat oven to 350°F (175°C). Grease or line a 9x13-inch baking dish with parchment paper.
In a large bowl, cream together the butter, brown sugar, and granulated sugar until light and fluffy.
Beat in the eggs one at a time, then mix in vanilla extract.
In a separate bowl, whisk together flour, crushed graham crackers, baking soda, and salt.
Gradually add the dry ingredients to the wet mixture until combined.
Press half the dough into the bottom of the prepared pan.
Sprinkle evenly with chocolate chips.
Carefully spread marshmallow creme over the chocolate layer. It's sticky, so using greased fingers or a spatula helps.
Drop spoonfuls of the remaining dough on top and gently spread or pat down to cover.
Bake for 25 minutes, or until golden brown on top.
Let cool in the pan for at least 20 minutes before cutting into bars.