Preheat your oven to 350°F (175°C).
Grease a 9x13 inch baking pan.
In a large saucepan, melt the butter over medium heat.
Remove the saucepan from heat and stir in the sugar until well combined.
Add the eggs, one at a time, mixing well after each addition.
Stir in the vanilla extract and mix until combined.
Sift together the flour, cocoa powder, and salt; then fold into the wet ingredients.
Fold in the chocolate chips, ensuring even distribution.
Pour half of the batter into the prepared pan, smoothing it evenly.
Add the mini marshmallows and graham cracker crumbs over the brownie layer.
Spread the remaining brownie batter over the marshmallows.
Bake in the preheated oven for 25-30 minutes.
Let the brownies cool completely in the pan before cutting into squares.