Make the Dough:
Mix discard, warm milk, sugar, egg, butter, and vanilla in a large bowl. Add flour and salt. Knead until dough is smooth and elastic (8–10 mins). Cover and let rise 1–1.5 hours.
Prepare the Filling:
In a bowl, combine marshmallows, chocolate chips, and crushed graham crackers.
Roll and Fill:
Roll risen dough into a 12x16-inch rectangle. Brush with melted butter. Sprinkle evenly with filling.
Cut and Stack:
Cut into 4 long strips, stack them, then cut into 6 squares. Turn and layer them vertically into a greased 9x5 loaf pan.
Second Rise:
Cover and rise again for 30–45 minutes.
Bake:
Preheat oven to 350°F (175°C). Bake 30–35 minutes. Tent with foil if browning too fast.
Add Toppings:
In the last 5 minutes, top with more marshmallows and graham crackers. Optional chocolate drizzle after baking.
Cool and Serve:
Let cool 10–15 minutes. Pull apart and enjoy warm!