1. Make the Pastry Cream

1. In the bowl of a stand mixer fitted with the whisk attachment, beat the egg yolks, sugar, cornstarch, vanilla powder, and salt until pale, light, and fluffy.
2. In a saucepan, bring the milk and heavy cream to a boil. Remove from the heat.
3. With the mixer running on medium speed, slowly pour the hot milk mixture into the egg yolk mixture. Mix until combined and slightly foamy.
4. Pour the mixture back into a clean saucepan. Cook over medium heat, whisking continuously, for 4–5 minutes or until thick enough to coat a spoon.
5. Immediately strain the pastry cream through a fine-mesh sieve into a clean bowl. Press plastic wrap directly onto the surface to prevent a skin from forming.
6. Refrigerate for 3–4 hours, or until completely chilled.

2. Make the Choux Pastry

1. Preheat the oven to 425°F. Line two baking sheets with parchment paper.
2. In a medium saucepan, combine the milk, water, butter, salt, and sugar. Bring to a rapid boil.
3. Remove the pan from the heat and add the Multi-Blend Flour all at once. Stir vigorously with a wooden spoon until the mixture forms a cohesive dough and a light film develops on the bottom of the pan.
4. Transfer the dough to the bowl of a stand mixer fitted with the paddle attachment. Mix on medium speed for a couple of minutes to release some steam and cool the dough slightly.
5. Add the eggs one at a time, mixing thoroughly after each addition. The dough may look separated at first but will come together as you continue mixing. Once all the eggs are incorporated, the dough should be smooth and fall from the paddle in a thick ribbon.
6. Transfer the dough to a piping bag fitted with a large round tip. Pipe 4-inch-long strips onto the prepared baking sheets, leaving at least 2 inches between each éclair.
7. Bake at 425°F for 10 minutes. Without opening the oven door, reduce the temperature to 350°F and bake for another 30 minutes, or until the éclairs are puffed, golden, and dry.
8. Remove from the oven and allow the shells to cool completely before filling.

3. Make the Chocolate Ganache

1. Place the chocolate and heavy cream in a heatproof bowl over a saucepan of gently simmering water. Make sure the bottom of the bowl does not touch the water.
2. Stir gently until the chocolate has melted and the mixture is smooth and glossy.
3. Remove from the heat and allow the ganache to cool slightly before using.

4. Fill the Éclairs

1. Whisk approximately ⅔ cup of the prepared ganache into the chilled pastry cream until evenly combined.
2. Transfer the chocolate pastry cream to a piping bag fitted with a long, narrow filling tip.
3. Make a small hole in the side of each cooled éclair and pipe in the filling until the éclair feels full.
4. Dip the top of each éclair into the remaining ganache, allowing excess chocolate to drip away.
5. Refrigerate until the ganache sets. Serve chilled or allow the éclairs to stand briefly at room temperature before serving.