Preheat oven to 425°F (220°C). Line two baking sheets with parchment paper and set aside.
Make the choux paste: In a medium saucepan, combine water, butter, sugar, and salt. Bring to a rolling boil over medium-high heat, stirring occasionally until butter melts completely.
Remove from heat and add all the flour at once. Stir vigorously with a wooden spoon until a smooth ball forms and pulls away from the sides of the pan, about 1 minute.
Return pan to medium-low heat and cook for 2 minutes, stirring constantly, to dry out the dough slightly. Transfer to a large bowl and let cool for 5 minutes.
Add eggs one at a time, beating well after each addition until fully incorporated. The dough should be smooth, glossy, and fall from the spoon in a thick V-shape.
Transfer dough to a piping bag fitted with a 1/2-inch round tip. Pipe 12 four-inch logs onto prepared baking sheets, spacing them 2 inches apart. Smooth any peaks with a wet finger.
Bake at 425°F for 15 minutes, then reduce heat to 350°F (175°C) and bake for 20-25 minutes more until deep golden brown and firm. Do not open the oven door during baking. Immediately poke a small hole in each end of every éclair and let cool completely on a wire rack.
Make the pastry cream: Heat milk in a medium saucepan over medium heat until steaming. In a separate bowl, whisk egg yolks, sugar, and cornstarch until pale and thick.
Slowly pour half the hot milk into the egg mixture while whisking constantly. Pour everything back into the saucepan and cook over medium heat, whisking constantly, until thickened and bubbling, about 3-4 minutes.
Remove from heat and whisk in butter, strained passion fruit pulp, and vanilla extract until smooth. Transfer to a bowl, press plastic wrap directly onto the surface, and refrigerate for at least 2 hours until completely cold.
To assemble, transfer chilled pastry cream to a piping bag fitted with a small round tip. Poke the tip into one end of each éclair and gently squeeze to fill until you feel slight resistance. Fill from the other end if needed.
Dust generously with powdered sugar just before serving. Serve chilled or at cool room temperature within 6 hours of filling for best texture.