Preheat oven to 400° F. Butter a large rimmed baking sheet, or use a Silpat liner.
In a saucepan combine the water, butter, sugar, and salt and bring to a boil. As soon as it boils, remove pan from the heat and add the flour all at once. Using a wooden spoon or spatula, briskly beat in the flour. Return the saucepan to the heat and continue briskly beating for two minutes. Remove from the heat again and let cool a minute or two.
Transfer the contents of the pan to a large bowl ("kitchen aid" if you have one). Add the eggs, one at a time, beating vigorously after each until smooth.
Transfer dough to a pastry bag with a 1/2" diameter plain tip (or use a zip lock bag with corner snipped). Pipe 2" diameter mounds about 2" apart on the pan—aim for 12. Bake until puffs are golden brown, 25 - 30 minutes. Transfer puffs to a rack and let cool completely.
Melt the chocolate in small bowl set in a pan of barely simmering water—do not let the water get into the chocolate or it will seize. Remove from heat.
Whip the cream until soft peaks just begin to form. Pour the melted chocolate into the whipped cream and continue to whip for a minute, until everything is evenly combined. Transfer chocolate cream to a clean pastry bag with a 1/2" plain tip, or go the simple route and use a spoon to fill the cream puffs.