Classic Eclairs

For the pastry cream

In a medium bowl, whisk the egg yolks, sugar, cornstarch, and salt until pale and light, about 1 minute. Nestle the bowl in a towel on the counter.

Put the milk and cream in a medium saucepan. Split and scrape the seeds from the vanilla bean half into the pan and whisk to break up the seeds, then drop in the pod. (If using extract, do not add it yet.) Bring to a simmer over medium heat. Slowly stream the hot milk mixture into the bowl of egg yolks, constantly whisking. Pour everything back into the pot and place back on medium heat. Cook, constantly stirring with a rubber spatula and scraping the bottom, until mixture is very thick about 1 minute. When the mixture begins to boil, cook for 1 minute more, still stirring. Remove from heat and scrape into a clean bowl. Discard vanilla pod. (If using vanilla extract, add it now and stir.) Cover the surface of the pastry cream with plastic wrap and cool completely in the refrigerator.

For the pastry
Preheat your oven to 425 degrees and position a rack in the middle position. In a medium or large bowl, whisk together the bread flour with the sugar and salt.

Add the butter and 1/2 cup of water to a medium saucepan over medium-high heat. Bring the water to a boil and when the butter is melted, add the flour mixture all at once. Stir vigorously with a wooden spoon until a smooth ball of dough forms and pulls away from the sides of the pot.

Dump the dough back into the bowl and stir with a wooden spoon for 30 seconds to release the steam. Add half the beaten eggs, stirring and beating vigorously until incorporated, then add the rest of the beaten eggs and stir until you form a smooth paste-like dough. Place the dough into a pastry bag fitted with a large, round tip.

Add a tiny dot of dough to the corners of a baking sheet and secure a piece of parchment. Pipe 12 thick, even lines of dough onto a parchment, 4-inches long and spaced at least 1½-inches apart. (See Cook’s Note.) Beat together with a tablespoon of water with the remaining egg white. Brush the tops of eclairs with the egg-white wash, using a pastry brush to smooth out any lumps.

Bake for 15 minutes — do not open the oven — then reduce the temperature to 350 degrees and bake an additional 22-25 minutes. The pastry will be browned and feel light, hollow, and dry when done. Transfer to a wire rack and let cool before filling.

For assembly
Put the chopped chocolate in a medium bowl. Heat the cream to a simmer in a small pan, then pour it over the chocolate. Let it sit for 30 seconds, then whisk until smooth.

Put the pastry cream into a pastry bag fitted with a small, round tip. Using a chopstick, punch a hole in each end of the pastry shells and push it to the middle. Fill the pastry shell by piping cream into each end (you may need to let the pastry cream warm a bit to flow easily). Dip the tops of each filled pastry into the chocolate, allowing the excess to drip off. Let the chocolate cool and set up slightly before serving. Voilà! Eclairs!

• Pastry cream can be made a day ahead and kept covered with plastic in the refrigerator until ready to use.
• Instead of making pastry cream, you can fill eclairs with a simple sweetened whipped cream.
• If you want to ensure all eclairs are evenly sized and spaced, you can draw 12 lines using a pencil and a ruler onto the parchment paper. Then flip the paper over to use the lines as a guide when piping.
• You can make the pastry dough ahead of time, pipe it onto parchment, and freeze. Once frozen, they can be removed and stored in a zip-top bag for up to 1 month. Bake them from frozen when you are ready to make your eclairs.