1. Prepare the Crust:

1. Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
2. In a saucepan, bring water and butter to a boil. Add flour and salt all at once, stirring vigorously until the mixture forms a ball. Remove from heat and let cool slightly.
3. Beat in eggs one at a time until the dough is smooth and glossy. Pipe 4-inch logs onto the prepared baking sheet.
4. Bake for 15 minutes, then reduce heat to 375°F (190°C) and bake for 20-25 minutes until golden brown. Cool completely.
5. For the pastry cream: Heat milk in a saucepan until steaming. Whisk sugar, egg yolks, and cornstarch in a bowl. Gradually whisk in hot milk, then return to saucepan and cook until thickened. Stir in vanilla and chill.
6. For the glaze: Heat cream until steaming, pour over chopped chocolate, and stir until smooth.
7. Fill eclairs with pastry cream and dip tops in chocolate glaze. Chill before serving.