Step 1: Preheat the Oven and Prepare the Pan
Preheat your oven to 350°F (175°C).
Line a 9×13-inch baking pan with parchment paper, leaving some overhang for easy removal.
Lightly grease the parchment paper.

Step 2: Make the Graham Cracker Crust
In a medium bowl, combine the graham cracker crumbs, melted butter, and granulated sugar.
Stir until the crumbs are evenly coated and resemble wet sand.
Press the mixture firmly into the bottom of the prepared pan to form a crust.
Bake for 8-10 minutes until lightly golden. Remove from oven and let cool slightly.

Step 3: Prepare the Brownie Batter
In a large bowl, whisk together the melted butter, granulated sugar, and brown sugar until well combined.
Add the eggs and vanilla extract, whisking until smooth and glossy.
In a separate bowl, sift together the flour, cocoa powder, salt, and baking powder.
Gradually fold the dry ingredients into the wet ingredients until just combined.
Be careful not to overmix to keep the brownies tender.

Step 4: Assemble the Brownies
Pour the brownie batter over the baked graham cracker crust, spreading it out evenly with a spatula.

Step 5: Bake the Brownies
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.
Do not overbake; you want them to stay fudgy.

Step 6: Add the S’mores Topping
Remove the brownies from the oven and immediately sprinkle the mini marshmallows, chocolate chips, and graham cracker pieces evenly over the top.
Return the pan to the oven and bake for an additional 5 minutes, just until the marshmallows are puffy and lightly golden.

Step 7: Cool and Slice
Allow the brownies to cool completely in the pan.
Use the parchment paper overhang to lift them out and slice into squares.

Step 8: Serve and Enjoy
Serve at room temperature or slightly warmed for an extra gooey treat!