Preheat the oven to 350°F. Line a 9-inch square baking pan with parchment or grease up using butter. Set aside.
In a large mixing bowl, whisk together softened butter, sugar, flour, egg, and vanilla extract until the ingredients are combined. Then, gently incorporate one cup of crushed graham crackers into the butter-sugar mixture. Add everything into the baking pan and press down to create an even layer.
Allow the mixture to bake for 10-12 minutes. After baking, allow the crust to cool for 15 minutes before adding the chocolate layer.
Once cooled, add the chocolate chips on top of the crust layer. Be sure to spread the chocolate chips evenly over the crust layer. Next, completely cover the chocolate layer with the remaining crushed graham crackers and mini marshmallows.
Place the pan back into the oven for another 5 minutes until the marshmallows are slightly golden and the chocolate is gooey.
Optional: After removing the pan from the oven, place the s’mores bar onto a cooling rack and top with more marshmallows. Use a hand torch to toast the marshmallows until they are campfire ready and enjoy!