Preheat your oven to 375°F (190°C).

Line a 9x13-inch baking pan with parchment paper.

Place a single layer of graham crackers at the bottom of the prepared pan.

In a large mixing bowl, cream together the unsalted butter, granulated sugar, and light brown sugar until light and fluffy. Add in the eggs and vanilla extract, mixing until well combined. In another bowl, whisk together the flour, salt, baking soda, chocolate chips, and mini marshmallows, then fold this mixture into the butter mixture gently.

Evenly distribute the cookie dough over the graham cracker layer. Sprinkle some mini marshmallows on top if desired.

Place your pan in the preheated oven and bake for 25-30 minutes until golden-brown.

Remove the pan from the oven and while warm, place the broken Hershey's chocolate bars on top to melt.

Let the bars cool for 20-30 minutes and then lift out using the parchment paper. Cut into squares and serve.