Preheat oven to 350F.
Slice the loaf of bread into 1-inch cubes, cutting off the crust. It will make about 10-11 cups of bread.
Place the bread cubes on a baking tray and bake for about 30 minutes, turning twice. (you can skip this step if you're tight on time, but the toasted bread makes this extra tasty!)
In a large bowl, whisk together the hot chocolate, eggs, vanilla, and salt. Set aside.
Place one layer of bread cubes into a 9x9 baking dish. Scatter the 1/4 cup chocolate chips and 1/4 cup mini marshmallows over the bread.
Top with the rest of the bread and pack tightly. Sprinkle with the remaining 1/4 chocolate chips and 1/4 cup marshmallows.
Pour hot chocolate mixture into the baking dish. The liquid should come to almost to the top of the dish with a bit of the bread still exposed. Cover with foil.
Refrigerate overnight or for at least 2 hours.
When ready to prepare, preheat oven to 325F. Allow the bread pudding to rest on the counter while oven heats.
Bake, uncovered, for 45-50 minutes or until the bread cubes are crisp and browned and a toothpick inserted into the middle is firm.
Remove the dish from the oven and top with the remaining 1 1/2 cups mini marshmallows.
Switch your oven settings to broil and broil for approximately 3-4 minutes or until the marshmallows are toasted to your liking. Watch it closely, the broiler can burn the marshmallows easily.
Let sit for about 20 minutes before serving, it will be very hot. Slice and serve. Enjoy!