01 -  Line a 20 cm square baking pan with parchment paper, ensuring an overhang on the sides for easy removal. 
 02 -  In a medium bowl, combine graham cracker crumbs, melted butter, and sugar. Mix until blended, then firmly press into the bottom of the pan to create an even layer. 
 03 -  Place 150 g mini marshmallows and 30 g unsalted butter in a microwave-safe bowl. Heat in 20-second intervals, stirring each time, until the marshmallows are fully melted and smooth. Evenly spread this mixture over the graham cracker base. Allow to cool for 5 minutes. 
 04 -  Combine chocolate chips and heavy cream in a microwave-safe bowl. Microwave in 20-second intervals, stirring until melted and glossy. Pour over the marshmallow layer and spread evenly. 
 05 -  Immediately sprinkle the remaining mini marshmallows, crushed graham cracker pieces, and optional chocolate chips over the chocolate layer. Gently press into the surface to adhere. 
 06 -  Refrigerate for at least 1 hour or until fully set. Use the parchment overhang to lift from the pan. Cut into squares and serve.