Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.

In a saucepan, bring water, butter, and salt to a boil over medium heat. Stir until butter is fully melted.

Reduce heat to low and add flour all at once. Stir vigorously with a wooden spoon until the mixture forms a smooth ball and pulls away from the sides of the pan.

Remove from heat and let cool slightly. Add eggs one at a time, beating well after each addition until the dough is smooth and glossy.

Pipe or spoon small mounds of dough onto the prepared baking sheet, spacing them about 2 inches apart.

Bake for 20-25 minutes until puffed and golden brown. Turn off the oven, leave the door slightly ajar, and let the profiteroles dry for 5 minutes. Remove and cool completely.

Fill each profiterole with vanilla pastry cream using a piping bag fitted with a small tip.

For the chocolate ganache, heat heavy cream until just boiling. Pour over chopped dark chocolate, let sit for 2 minutes, then stir until smooth. Drizzle over filled profiteroles.