Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.

1. In a medium saucepan, combine the water, butter, salt, and sugar. Heat over medium-high heat, stirring occasionally until the butter melts and the mixture begins to simmer.
2. Add the flour all at once, stir vigorously until the mixture forms a ball and pulls away from the sides of the pan. Cook for another 1-2 minutes, then remove from heat. Let the dough cool for 5 minutes.
3. Add the eggs one at a time, mixing well after each addition. The dough should be smooth, thick, and shiny.
4. Spoon or pipe spoonfuls of dough onto the prepared baking sheet, spacing them about 2 inches apart. Wet your finger to smooth any peaks on top.
5. Bake for 20-25 minutes, or until golden and puffed up. Do not open the oven door during the first 15 minutes.
6. Remove the profiteroles from the oven and make a small slit in the side to allow steam to escape. Cool completely on a wire rack.
7. For the whipped cream filling, beat heavy cream with powdered sugar and vanilla until stiff peaks form. For pastry cream, prepare it ahead of time and refrigerate until cool.
8. For the ganache, heat the cream in a saucepan until simmering, then remove from heat and stir in the chopped chocolate until smooth.
9. Fill each cooled profiterole with whipped cream or pastry cream. Drizzle with chocolate ganache or dip the tops into it.
10. Serve immediately or refrigerate for up to 2 hours before serving.