• Preheat oven to 425 degrees.

Custard

• Warm the milk and vanilla extract in a saucepan. Then, whisk the egg yolks and sugar in a bowl until thickened. Sift the cornstarch in and whisk until everything is smooth and well combined. Add 1/4 cup of the warm milk into the mixture and whisk. Add the remaining milk slowly while whisking. 
• Return pan to medium-high heat, whisking constantly until mixture thickens. Remove from the heat and stir in the butter.
• Let the custard cool and cover it with plastic wrap. Press the plastic against the surface to prevent a skin from forming on top. Chill for at least 2 hours if serving same day or store in the refrigerator overnight.

Pastry

• In a large saucepan over medium heat, add water, butter, sugar, vanilla and salt. Bring to a boil. Then turn off heat, add flour and stir with a wooden spoon until thickened. Allow dough to cool for 10 minutes.
• Add eggs one at a time, beat in with hand mixer or whisk. The texture of the dough should be smooth and fall slowly from the whisk when lifted out of the bowl. Transfer dough to a piping bag with a large star tip.
• Pipe the dough onto a lined baking sheet, leaving 2 inches of space in between each one. Make lines about the size of hot dogs for eclairs and big dots for cream puffs.
• Egg Wash: In a bowl, whisk egg and water together. Brush the surface of each eclair with the egg wash. This will smooth out any imperfections so that they can look beautiful once baked.
• Bake 12-15 minutes, then reduce the heat to 375 degrees and bake until puffed up and light golden brown, about 18-25 minutes more, depending on your oven and size of your pastries.
• Allow pastries to cool on a cooling rack.
• Use a thin piping tip like Ateco 230 to poke 3 holes in the bottom of each eclair and fill with custard. The eclair should feel heavy when full.
• For the cream puffs, just poke 1 hole in the bottom and fill with the custard or make a chantilly cream by combining vanilla extract and whipped cream. Sprinkle the cream puffs with powdered sugar.

Chocolate ganache

• In a small sauce pan, bring the cream to a boil. Turn off heat.
• Put the chocolate in a medium size bowl. Pour the hot cream over the chocolate and whisk until melted and smooth.
• Dip the tops of the eclairs in the warm chocolate glaze and set on a sheet pan or cooling rack.