Step 1: Preheat the Oven
• Preheat Oven: Preheat your oven to 350°F (175°C).
• Prepare Baking Dish: Grease a 9×13-inch baking dish or line it with parchment paper for easy removal.

Step 2: Make the Crust
• Combine Ingredients: In a medium bowl, mix together the graham cracker crumbs, cocoa powder, melted butter, and granulated sugar until well combined.
• Press into Dish: Press the mixture evenly into the bottom of the prepared baking dish to form a crust.

Step 3: Layer the Filling
• Add Chocolate Chips: Sprinkle the semi-sweet chocolate chips evenly over the crust.
• Add Marshmallows: Next, add the mini marshmallows on top of the chocolate chips.
• Add Nuts (if using): If you’re using nuts, sprinkle them over the marshmallows.

Step 4: Pour Sweetened Condensed Milk
• Drizzle Milk: Pour the sweetened condensed milk evenly over the entire layer, making sure to cover as much of the marshmallows and chocolate as possible.

Step 5: Bake
• Bake: Bake in the preheated oven for 25–30 minutes, or until the edges are golden and the marshmallows are toasted.
• Add Mini Chocolate Chips: In the last 5 minutes of baking, sprinkle the mini chocolate chips on top and return to the oven until melted.

Step 6: Cool and Cut
• Cool: Remove from the oven and let the bars cool in the pan for at least 30 minutes before cutting.
• Cut into Bars: Once cooled, lift the bars out of the pan using the parchment paper (if used) and cut them into squares or rectangles.