Begin by preheating your oven to 350°F (175°C). Prepare an 8x8 inch baking pan by greasing it lightly and lining it with parchment paper. Ensure there's an overhang on two opposite sides for easier removal after baking.
In a medium mixing bowl, combine the graham cracker crumbs, melted butter, and brown sugar. Stir the mixture until all ingredients blend together smoothly into a wet crumbly texture.
Press this graham cracker mixture evenly and firmly into the bottom of your prepared baking pan to form a solid crust. Bake in the preheated oven for 10 minutes, or until the crust is lightly golden and set.
While the crust bakes, take a separate bowl and whisk together the all-purpose flour, baking powder, and salt until well combined. This will create a light and airy layer for the bars.
After the crust is baked, carefully remove it from the oven. Evenly scatter the semi-sweet chocolate chips over the warm crust, allowing them to start melting slightly.
Next, sprinkle the mini marshmallows evenly over the layer of chocolate chips. If you choose to include it, add the sweetened shredded coconut on top for a delightful tropical twist.
Gently pour the flour mixture over the layers of marshmallows and chocolate chips to create a final topping. Take care to spread it out evenly without stirring or mixing the layers together.
Return the pan to the oven and bake for an additional 15-20 minutes. You’ll know it’s ready when the top is golden brown and the marshmallows are puffed up and lightly toasted.
Once baked, remove the bars from the oven and allow them to cool in the pan for at least 10 minutes. Then, use the overhanging parchment paper to lift the bars out of the pan.
Cut into squares, and serve either warm or at room temperature for an excellent treat.
Notes
Serve on a rustic wooden board and sprinkle extra graham cracker crumbs and chocolate chips on top for an inviting look.