In a saucepan, combine the water and butter. Bring to a boil over medium heat, stirring until the butter has melted.

Add the flour and salt all at once, stirring vigorously until the dough forms a ball. Cook for 2 minutes.

Transfer the dough to a bowl and let it cool for a few minutes. Incorporate the eggs one at a time, mixing until the dough is smooth and shiny.

Preheat the oven to 425°F (220°C). Pipe the dough onto a parchment-lined baking sheet in 4-inch lengths.

Bake for 20-25 minutes until golden brown and puffed. Let cool completely.

In a saucepan, heat the milk until just boiling. In another bowl, whisk together sugar, cornstarch, and egg yolks.

Gradually add the hot milk to the egg mixture, whisking continuously. Return to the saucepan and cook until thickened, about 2 minutes. Stir in vanilla and butter.

Pour into a bowl, cover with plastic wrap (press directly onto the surface), and refrigerate until cool.

Once the shells are cool, carefully slice them open. Fill each shell with pastry cream using a piping bag.

For the chocolate glaze, melt the chocolate chips and butter until smooth, then dip the top of each éclair into the glaze.