1. Preheat oven to 350°F (175°C). Line a 9×13-inch baking pan with parchment paper and lightly grease. 2. In a large bowl, cream together butter, brown sugar, and granulated sugar until light and fluffy. Beat in eggs one at a time, then mix in vanilla. 3. In another bowl, whisk together flour, baking soda, salt, and graham cracker crumbs. Gradually add to wet ingredients and mix until combined. 4. Press two-thirds of the dough evenly into prepared pan. Sprinkle chocolate chips over dough, then top with marshmallows. Crumble remaining dough over top, leaving some marshmallow and chocolate exposed. 5. Bake 25–30 minutes, until edges are golden and center is just set. Cool completely before slicing into bars.