Preheat your oven to 350°F (175°C). Line a 9x13-inch baking dish with parchment paper, leaving some overhang for easy removal later.
In a medium saucepan, melt the butter over medium heat. Once melted, stir in the brown sugar, vanilla extract, and salt until well combined. Bring the mixture to a gentle boil and let it boil for 2 minutes, stirring constantly.
Remove the saucepan from heat and stir in the graham cracker crumbs until fully coated.
Press the graham cracker mixture evenly into the bottom of the prepared baking dish.
Bake in the preheated oven for 10 minutes. Remove from the oven and sprinkle the mini marshmallows and chocolate chips evenly over the top.
Return to the oven and bake for an additional 5 minutes, or until the marshmallows are golden brown and the chocolate is melted.
Allow the dish to cool completely at room temperature, then refrigerate for at least 1 hour to set.
Once set, lift the parchment paper to remove the S'mores Crack from the dish. Cut into squares and serve.