Preheat your oven to 425°F (220°C) and line two baking sheets with parchment paper. In a medium saucepan, combine 1 cup of water, 1/2 cup of unsalted butter, and a pinch of salt. Bring to a boil over medium heat, then swiftly stir in 1 cup of all-purpose flour, mixing until a smooth ball forms. Allow it to cool for 5 minutes before adding 4 large eggs, one at a time, beating until glossy. Pipe the batter into 4-inch logs on the prepared sheets and bake for 15 minutes. Reduce the temperature to 350°F (175°C) and bake for an additional 15 minutes until golden and puffed. Let the choux cool completely.

In a saucepan, heat 2 cups of whole milk with 1/2 cup of granulated sugar until just bubbles form at the edges, but don’t boil. Meanwhile, whisk together 4 large egg yolks and 1/4 cup of cornstarch until smooth. Gradually pour the hot milk into the egg mixture, whisking constantly to temper the eggs. Return the mixture to the stove over medium heat and stir until it thickens, about 5 minutes. Remove from heat, stir in 1 teaspoon of vanilla extract, and let cool before covering with plastic wrap directly on the surface. Chill in the fridge for at least 2 hours.

In a small saucepan, heat 1/2 cup of heavy cream and 1 tablespoon of butter over medium heat until it simmers gently. Remove from heat and pour this hot mixture over 8 ounces of finely chopped dark chocolate in a bowl. Let it sit for 5 minutes to melt the chocolate, then whisk until smooth and glossy. If you prefer a thicker glaze, allow it to cool slightly to thicken up before using.

Once the choux pastry and cream filling are cooled, slice each éclair shell lengthwise or cut a slit in the side. Using a piping bag fitted with a round tip, pipe in the chilled pastry cream until filled. Dip the tops of each filled éclair into the chocolate glaze, allowing excess glaze to drip off. Place the éclairs on a wire rack and let the glaze set for about 10 minutes before serving. Enjoy your homemade Chocolate Éclairs!