Preheat your oven to 350°F (175°C). Grease or line an 8x8-inch baking pan with parchment paper.

Make the Brownie Batter:

In a mixing bowl, combine the melted butter and granulated sugar. Mix until smooth.

Add the eggs and vanilla extract, then whisk until well combined.

Stir in the cocoa powder, flour, salt, and baking powder until just combined (do not overmix).

Bake the Brownies:

Pour the brownie batter into the prepared baking pan and spread evenly.

Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

Add Toppings:

Remove the brownies from the oven and immediately sprinkle the mini marshmallows and chocolate chips evenly over the top.

Sprinkle the crushed graham crackers over the marshmallows and chocolate chips.

Finish Baking:

Return the brownies to the oven and bake for an additional 5-7 minutes, or until the marshmallows are golden and the chocolate is melted.

Cool and Serve:

Allow the brownies to cool in the pan for about 10 minutes before cutting into squares. Serve warm or at room temperature.