- In a small pot off the heat, whisk together the sugar and flour. Add the eggs and vanilla. Mix well. Add the hot milk. Bring to a boil over medium heat, whisking constantly and scraping the sides and bottom of the pot, until thickened. Let simmer for 1 to 2 minutes over low heat. Remove from the heat. Add the butter.
- Strain the cream through a sieve, if needed. Transfer to a bowl and cover with plastic wrap directly on the surface of the cream. Let cool. Refrigerate for 2 hours or until completely chilled. When ready to use, mix with a spatula until creamy and smooth.
- With the rack in the middle position, preheat the oven to 375°F (190°C). Line a baking sheet with a silicone mat or parchment paper.
- In a pot, bring the water, butter and salt to a boil. Remove the pot from the heat. Add the flour all at once and stir vigorously with a wooden spoon. Return the pot to medium heat and cook, stirring, until the mixture forms into a ball and detaches from the sides of the pot, about 2 minutes.
- Remove the pot from the heat and add the eggs, one at a time, mixing between each addition until the mixture is smooth.
- Transfer into a pastry bag fitted with a ¾-inch (2 cm) plain tip. Pipe 12 cream puffs onto the baking sheet, spacing them out. You can freeze the cream puffs at this point, if desired (see note).
- Bake for 25 minutes. Reduce the oven temperature to 275°F (135°C) and bake for another 20 minutes. Let cool completely on a wire rack.
- Cut off the top of each cream puff and remove any dough from the middle that has not completely dried out. Fill with the chilled pastry cream. Close the cream puffs with their tops. Using a spoon, drizzle the melted chocolate over the cream puffs.
Raw choux pastry freezes very well once piped out onto the baking sheet. When ready to use, it is best to thaw the cream puffs before following the baking instructions above.