Preheat your oven to 350°F (175°C) and grease a 9-inch pie dish.
In a large mixing bowl, whisk together the melted butter and granulated sugar until smooth.
Beat in the eggs one at a time, then stir in the vanilla extract.
In another bowl, sift together the flour, cocoa powder, baking powder, and salt. Gradually add this dry mixture to the wet ingredients, stirring until just combined.
Fold in the semi-sweet chocolate chips for added richness.
Pour half of the brownie batter into the greased pie dish, smoothing it out with a spatula.
Sprinkle the graham cracker crumbs evenly over the first layer of brownie batter.
Add the mini marshmallows on top of the graham cracker crumbs.
Pour the remaining brownie batter over the marshmallows, spreading it evenly.
Crush the whole graham crackers and sprinkle them over the top of the brownie pie.
Bake in the preheated oven for about 30-35 minutes, or until a toothpick inserted in the center comes out with moist crumbs (not wet batter).
Remove from the oven and allow to cool slightly before serving.
Notes
Serve warm with a scoop of vanilla ice cream on the side and drizzle with chocolate sauce for an extra indulgent treat.