Step 1: Preheat your oven to 350°F (175°C) to ensure even baking.
Step 2: Melt the butter in your skillet over low heat, then stir in the chocolate chips until smooth.
Step 3: Mix in the sugar, vanilla extract, and coffee granules until combined.
Step 4: Incorporate the eggs one at a time, mixing well after each addition.
Step 5: In a separate bowl, whisk together the flour, cocoa powder, and baking powder, then fold into the wet mixture.
Step 6: Add the Hershey chocolate pieces and graham crackers, folding gently.
Step 7: Pour the brownie batter into the skillet and spread evenly.
Step 8: Bake in the preheated oven for 20-25 minutes until a toothpick comes out with a few moist crumbs.
Step 9: Spread marshmallow fluff over the warm brownies, or add marshmallows.
Step 10: Broil for 1-2 minutes until the marshmallows are golden brown.
Step 11: Allow to cool slightly before serving warm from the skillet.