Preheat the oven to 350 F. In a large bowl, whisk together brown sugar, melted butter, eggs, and vanilla extract. Add in the flour, salt, and baking powder, and mix until smooth.
Fold in the chocolate chips, mini marshmallows, and crushed graham crackers. Spread the mixture into a greasd 8-inch square baking dish. Bake for 20-25 minutes.