Traditional Eclairs with Cream Filling

Instructions
Step 1: Make the Pastry Cream (Filling)
Heat the Milk: In a medium saucepan, heat the milk over medium heat until just simmering.
Mix Egg Yolks and Sugar: In a separate bowl, whisk the egg yolks, sugar, cornstarch, and salt together until pale and smooth.

Temper the Eggs: Slowly pour half of the hot milk into the egg mixture while whisking constantly to temper the eggs. Then pour the tempered mixture back into the saucepan with the remaining milk.
Thicken the Cream: Cook the mixture over medium heat, whisking constantly, until it thickens and begins to bubble (about 2-3 minutes).
Remove from Heat: Remove from heat and whisk in the butter and vanilla extract. Transfer to a bowl and cover with plastic wrap (touching the surface to prevent a skin from forming). Let it cool completely in the refrigerator for at least 2 hours.
Step 2: Make the Choux Pastry
Preheat the Oven: Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
Cook the Dough: In a medium saucepan, combine the butter, water, sugar, and salt. Bring to a boil over medium heat. Once boiling, add the flour all at once and stir vigorously with a wooden spoon until the dough pulls away from the sides and forms a ball. Continue cooking and stirring for about 2 minutes to dry out the dough.
Add the Eggs: Remove the dough from the heat and let it cool slightly for 3-4 minutes. Add the eggs one at a time, beating well after each addition until the dough is smooth and shiny.
Pipe the Dough: Transfer the dough to a piping bag fitted with a large round tip. Pipe 4-5 inch strips onto the prepared baking sheet, spacing them a couple of inches apart.
Bake: Bake for 15 minutes at 400°F, then reduce the temperature to 350°F (175°C) and bake for an additional 20-25 minutes, or until the eclairs are puffed and golden brown. Turn off the oven and leave the eclairs inside with the door slightly ajar for 10 minutes to dry out.
Cool: Remove from the oven and let cool completely on a wire rack.