2Preheat your oven to 425°F (220°C). Line a baking sheet with parchment paper.
In a medium saucepan, bring 1 cup of water and 1/2 cup of unsalted butter to a boil over medium heat.
Add 1 cup of all-purpose flour all at once and stir vigorously until the mixture forms a ball and pulls away from the sides of the pan.
Remove from heat and let the mixture cool for 5 minutes.
Add 4 large eggs, one at a time, beating well after each addition until the dough is smooth and shiny.
Drop the dough by tablespoonfuls onto the prepared baking sheet, spacing them about 2 inches apart.
Bake for 20-25 minutes, or until the puffs are golden brown and sound hollow when tapped. Remove from the oven and let cool completely on a wire rack.
In a medium bowl, whip 1 cup of heavy cream with 2 tablespoons of powdered sugar and 1 teaspoon of vanilla extract until stiff peaks form.
Melt 1/2 cup of dark chocolate in a microwave-safe bowl in 30-second intervals, stirring after each interval until smooth.
Cut the cooled puffs in half horizontally and fill each with a generous dollop of whipped cream.
Drizzle the melted dark chocolate over the filled cream puffs.
Serve immediately or refrigerate until ready to serve.