Start with the pastry cream as it needs 2 hours to chill after being made.

Combine the milk and half of the sugar in a medium saucepan. Heat over low heat and scald. The sugar will be dissolved in the milk.

In a medium bowl whisk together the cornstarch and the remaining sugar. Add the eggs and egg yolks. Whisk well to combine.

Slowly add the scalded milk to the eggs, whisking constantly. Return the egg mixture to the saucepan and heat over medium. Again, whisking constantly until the mixture thickens into a custard. It will take a bit and then turn quickly. Remove from the heat and continue whisking.

Add the vanilla extract and butter. Whisk until fully combined.

Pour the custard onto a plastic wrap lined baking sheet and spread out evenly. Cover with another layer of plastic wrap to prevent a skin from forming. Place in the refrigerator a minimum of 2 hours before transferring to a piping bag with a medium circular tip.

Preheat the oven to 375F.

In a medium saucepan combine the water, butter, and salt. Heat over low heat until the butter is melted.

Add the flour all at once and begin to stir with a wooden spoon. Stir until no dry spots remain and lumps are minimal. The dough will begin to pull away from the walls of the saucepan.

Increase the heat to medium and continue to stir constantly until a starchy film starts to form on the bottom and sides of the saucepan.

Transfer the dough to a stand mixer bowl fitted with a paddle attachment. Mix on low until the steam dissipates and the dough has cooled to 120F.

Add the eggs one at a time on low speed and allow them to incorporate fully before adding the next. Scrape the sides of the bowl and the paddle after a few eggs. Once the dough begins to look like a wet brownie batter, stop adding eggs and test.

Test the dough by dipping the paddle into the dough and pulling it out. It should look smooth, shiny, and not fall off the paddle. It should retain its shape while being moist.

Transfer half of the dough to a large pastry bag fitted with a large circular tip. Pipe straight lines onto a parchment lined baking sheet, providing about 1 inch between each.

Repeat with the remaining dough. Optional: Egg wash the dough before baking (not shown here).

Bake at 375F for 40 minutes. Pate a choux should be puffy and golden brown, and the interior cracks should not look wet.

Cool completely before filling.

Chop the chocolate into small pieces. Add to a medium bowl and pour heavy cream over the chocolate. Microwave for 30 second intervals, about 1 minute.

Stir to combine. Once a smooth consistency is achieved, add the butter and stir until combined.

Use a medium circular piping tip to remove a hole from the bottom of the eclair.

Place the tip of the piping bag containing the pastry cream into the eclair and gently fill with cream. You can feel the eclair filling in your hand. Careful not to over fill.

Dip the eclair in chocolate, top side down or spread over the top using a spoon.

Allow to set for a few minutes and the chocolate will become shiny.