Preheat oven to 350°F and line a 9 x 9-inch pan with nonstick spray and parchment paper.
In a medium mixing bowl, combine the all-purpose flour, graham cracker crumbs, baking soda, and salt, then set aside.
In a large mixing bowl, whisk together the butter, brown sugar, and granulated sugar until the mixture begins to lighten in color, about 1-2 minutes. Add the eggs one at a time, followed by the vanilla extract. Slowly stir in the flour mixture just until combined. Spread 3/4 of the dough into the prepared pan. Lightly wet your hands and press the dough into an even layer.
Sprinkle the Hershey bars, mini marshmallows, and regular marshmallows over the top of the graham cracker cookie dough. Drop spoonfuls of the remaining cookie dough over the marshmallows.
Bake for 35 to 40 minutes, until golden brown. Let the bars cool for 10 minutes before cutting.