Preheat the oven to 375°F and line a 13x9-inch baking pan with parchment paper, leaving an overhang of 2 inches on the sides.

Place 7-8 rectangles of unbroken graham crackers on the bottom of the pan, breaking them if necessary to fit.

In the bowl of an electric mixer fitted with the paddle attachment, cream the butter, granulated sugar, and brown sugar until light and fluffy.

Add the eggs and vanilla extract to the creamed mixture and mix until well combined.

In a separate bowl, whisk together the flour, salt, and baking soda.

Gradually add the flour mixture to the creamed mixture, mixing just until combined. Stir in the chocolate chips and mini marshmallows.

Spread the dough over the graham crackers, pressing it flat. Top with additional marshmallows if desired.

Bake the bars for 25-30 minutes, until golden brown and a toothpick inserted in the center comes out clean. If necessary, cover the bars with foil if they're browning too quickly.

While the bars are still warm, place the broken chocolate bar pieces on top. The heat will melt the chocolate.

Allow the bars to cool for 20-30 minutes before lifting them out of the pan by the parchment paper overhang. Cut into squares and serve. Note: The chocolate may remain soft and melty at room temperature.