01 -
Preheat the oven to 350°F (175°C).
02 -
In a large mixing bowl, whisk together graham cracker crumbs, unsweetened cocoa powder, and powdered sugar until evenly blended.
03 -
Pour melted unsalted butter and sweetened condensed milk into the dry mixture; stir thoroughly until fully combined.
04 -
Gently fold in mini marshmallows, chocolate chips, and optional chopped nuts until evenly distributed throughout the batter.
05 -
Lightly grease a baking pan and spread the mixture evenly inside, smoothing the surface.
06 -
Bake in the preheated oven for 25 to 30 minutes, until edges are firm and the center is slightly set but still soft.
07 -
Allow bars to cool completely in the pan before cutting into squares to ensure clean slices.