Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan.
In a large bowl, whisk together the melted butter and granulated sugar until well combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
In another bowl, sift together the flour, cocoa powder, baking powder, and salt. Gradually fold the dry ingredients into the wet mixture until just combined.
Gently fold in the chocolate chips. Pour the brownie batter into the prepared baking pan and spread it evenly.
Bake in the preheated oven for 25-30 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.
Remove the brownies from the oven and immediately sprinkle the mini marshmallows and crushed graham crackers on top. Drizzle the chocolate syrup over the marshmallows.
Return the pan to the oven and bake for an additional 5-7 minutes, until the marshmallows are lightly golden and puffed.
Allow the brownies to cool in the pan for at least 15 minutes before cutting them into bars.
Notes
Serve the brownie bars warm, topped with extra mini marshmallows and a drizzle of chocolate syrup for an indulgent treat!