Preheat the oven to 210°C and line a baking tray with baking paper.
Combine the milk, water, butter, and salt in a pan. Heat slowly until the butter is fully melted and the mixture just begins to boil.
Remove the pan from the heat, add the flour all at once, and stir vigorously until the mixture is smooth and fully combined.
Return the pan to medium heat and stir continuously for 2–3 minutes. The dough should form a ball, sizzle slightly, and stick lightly to the bottom of the pan.
Transfer the dough to a bowl and let it cool slightly. Gradually add the eggs, one at a time, mixing thoroughly after each. Adjust with the fourth egg or half of it if necessary, ensuring the dough is smooth and pliable.
Transfer the dough to a piping bag with a smooth nozzle (10–12 mm). Pipe 2 cm-wide and 2 cm-tall rounds onto the prepared baking tray, leaving space between each. Alternatively, shape using two spoons. Use a wet finger to flatten any peaks on the tops of the profiteroles for an even finish.
Bake in the preheated oven for 20–25 minutes, or until golden brown. Let the profiteroles cool completely before filling or glazing.
In a heatproof bowl, combine the whipped cream, dark chocolate, and powdered sugar. Heat over a bain-marie (double boiler) until smooth. Remove from heat and stir briefly to finish.
Beat the whipped cream with the sugar (and whipped cream stiffener, if using) until stiff. Transfer to a piping bag with a small smooth nozzle.
Poke a small hole in the bottom of each profiterole and fill with whipped cream using the piping bag.
Dip the tops of the profiteroles into the chocolate glaze. Place them on a baking sheet or plate and refrigerate until the glaze sets.
Dip the tops of the filled profiteroles into the prepared chocolate glaze. Place the glazed profiteroles on a baking sheet or plate and refrigerate until the chocolate sets.
Sprinkle the glazed profiteroles with chopped nuts for decoration.