Preheat oven to 400 degrees F.
In a saucepan over medium heat, heat water, salt, sugar, and butter. Bring to a rolling boil and remove from heat.
Add flour and stir with wooden spoon until fully incorporated (30-60 seconds).
Let sit for 3 minutes to cool slightly.
Move dough to bowl of electric mixer fit with paddle attachment.
With mixer on low to medium, add eggs (one at a time) until fully incorporated.
Dough should be glossy and thick and fall slowly from paddle.
Fill piping bag with round tip with batter. Pipe cream puffs (1 1/2" to 2") leaving space between each for spreading.
Whisk additional egg and brush dough with egg (push down points).
Bake for 15 minutes and then reduce heat to 375 F. Bake for an additional 10 to 15 minutes or until cream puffs are golden brown. Do not open the oven during baking.
Remove from heat and allow to cool.
Slice each cream puff in half.
In saucepan, simmer heavy cream and stir in chocolate and butter. Stir until smooth.
Dip cream puff tops in ganache and set aside to set.
Fill bottoms with marshmallows and place in oven set to broil (450 degrees F). Watch carefully. One marshmallows start to toast (30 seconds), remove from oven. Press down slightly with top of cream puff.
Garnish with edible gold leaf.