Make the pastry cream

• Place the vanilla bean and its scrapings in a saucepan in a pot on the stove with the milk. Begin heating the milk and vanilla over medium heat.
• Prepare an ice bath large enough to receive the saucepan.
• In a large bowl, whisk together the egg yolks, sugar, starch, and salt. Whip it well with a hand whisk. It should become pale yellow and homogenous.

• When the milk comes to a boil, turn off the heat.
• Ladle about 1/3 of the milk into the egg mixture, whisking, to temper the eggs.

• Pour the egg/sugar/milk mixture into the rest of the hot milk and return the pot to heat.
• Cook over medium-low to medium heat until the temperature reaches 185°F (85°C). Don’t let it boil hard or it may curdle! Some bubbling is ok.

• Remove the saucepan to the ice bath and stir it once or twice to stop the cooking. Beat the butter into the still-warm custard.
• Strain the pastry cream through a fine sieve, pressing with a silicone spatula, onto a baking sheet covered with parchment paper. Flatten the cream out, cover it with plastic wrap, and refrigerate it until ready to use.

Make the eclair pastries

• Preheat your oven to 425°F (218°C).
• In a saucepan, combine the water or milk, butter, salt, and sugar. Heat over medium-high until all the butter is melted and the liquid is boiling well.
• Add the flour all at once and stir with a wooden spoon, keeping the mixture over medium heat.
• Cook until the temperature of the dough reaches 175°F (79°C) and the dough behaves like a fairly cohesive ball.

• Transfer the dough to a stand mixer and beat until the dough cools to 145°F (63°C).
• Add the eggs, one at a time, while beating the dough on medium-high speed. Mix each egg in completely before adding the next. Scrape the bowl between additions.

• Transfer the dough to a piping bag fitted with a 1/2″  closed-star tip.
• Draw 12–14 straight lines, each 4.5″ long on 2 pieces of parchment. Tack those down to a pan, marked-side-down, with a small squirt of the choux paste in each corner.

• Pipe one pan full of pastries by holding the tip of the pastry bag about 1/2″ from the surface of the pan, the bag held at 45°, and piping dough onto the pre-drawn lines. Don’t go too fast or your pastries will be tiny and thin. Don’t go too slow or you’ll run out of dough and they’ll be too fat. Shoot for about 1″ wide
• Bake the first pan of dough on the center rack for 15 minutes at 425°F (218°C), then turn the heat down to 350°F (177°C), turn the pan around in the oven, and bake another 15 minutes.
• Pastries should be beautifully golden. Remove them from the oven to cool.

• Reheat the oven to 425°F (218°C), pipe out your second tray of pastries, and bake them the same way.

Assemble the eclairs

• Transfer the pastry cream to a piping bag fitted with a 1/4″ plain tip.
• Use a chopstick or another long, thin instrument to poke into one end of each eclair. Push the stick through to the opposite end of the pastry (don’t break through on the other side). Wiggle it around inside as you move through it, making space for the pastry cream.
  • If the pastry is misshaped on the bottom so that putting a stick through the whole thing won’t work, cut two small holes, one towards each end, on the bottom of the pastry and fill into the halves through those holes.

• Insert the tip of the piping bag into the hole you made and gently squeeze the pastry cream into the eclair. Hold the pastry vertically so that gravity is on your side. Fill all the pastries.

• Make the ganache by combining the chocolate, butter, corn syrup, and salt in a heatproof bowl that is big enough to fit an eclair into. Microwave in 30-second intervals, stirring between, until the ganache is smooth and homogenous.
• Dip each eclair into the ganache and use a spatula to remove excess chocolate and spread it evenly across the surface. (Or if the chocolate has cooled slightly, use the spatula to apply it.)

• Serve your eclairs!