Preheat oven to 350°F(175°C).
In a food processor, combine graham crackers and sugar. Pulse to crumble. Stir in melted butter.
Press the graham cracker crumble into an ungreased 13x9” baking pan. Bake until lightly browned, 7-9 minutes. Set aside to cool.
For brownies, melt unsweetened chocolate on high in the microwave, stirring every 15 seconds. Cool slightly.
In a mixing bowl, combine the butter and sugar and beat on medium speed until light and fluffy, 5-7 minutes.
Add eggs, 1 at a time, beating well after each addition.
Then beat in the melted chocolate and vanilla.
In another bowl, whisk together flour, cocoa, baking powder and salt; stir that into the creamed mixture. Fold in 1 cup miniature marshmallows.
Spread batter over graham cracker crust. Top with 1 cup marshmallows and broken graham crackers. Bake just until the center is set, 25-30 minutes.