In a saucepan, combine the water, milk, unsalted butter, and salt. Heat over medium until the butter melts.

Reduce heat and stir in the flour all at once. Stir aggressively until you form a smooth dough.

Remove from heat and let the dough cool slightly. Gradually add eggs, mixing until smooth and glossy.

Preheat your oven to 400°F (200°C). Pipe mounds of dough onto a baking sheet lined with parchment paper.

Bake until golden brown, being careful not to overbake to avoid dryness.

In another saucepan, whisk together milk, egg yolks, sugar, and cornstarch. Cook while whisking until thickened and creamy.

Once cooled, slice the profiteroles in half or use a piping bag to fill them with custard.

Heat heavy cream until hot but not boiling and pour it over chopped dark chocolate. Stir until smooth.

Drizzle the chocolate sauce over filled profiteroles and serve immediately.