Combine Ingredients: In a medium saucepan over medium heat, combine the butter, water, milk, salt, and sugar.

Incorporate Flour: Reduce the heat to low and add the flour all at once. Stir until the flour is completely incorporated and a thick dough forms a ball.

Mix the Dough: Transfer the dough to a stand mixer and turn it on low. Add the eggs one at a time, allowing each egg to fully incorporate before adding the next.

Prepare for Piping: Transfer the dough to a piping bag fitted with a large tip.

Pipe the Dough: Pipe the dough into 4-inch strips on a silicone baking sheet, spacing them about 2-3 inches apart. Brush gently with egg wash.

Bake: Bake at 400°F for 20 minutes, then reduce the heat to 350°F and bake for another 10-15 minutes until golden. Allow the éclairs to cool completely before filling.

Heat the Milk: In a medium saucepan, heat the milk and vanilla over medium heat until it reaches a low boil.

Prepare Egg Mixture: In a separate bowl, whisk together the egg yolks and sugar to create a paste. Add the cornstarch and stir to incorporate.

Combine Mixtures: Slowly pour the hot milk into the egg mixture, whisking constantly to prevent the eggs from curdling.

Thicken the Cream: Return the mixture to the saucepan and bring it to medium heat, whisking constantly. The mixture will thicken and come to a boil.

Finish the Cream: Remove from heat and fold in the butter, stirring until it is completely melted. Cover the cream tightly with plastic wrap and allow it to cool before transferring to a piping bag.

Fill the Éclairs: Use a small, pointy piping tip and piping bag to fill the éclairs with the cooled vanilla pastry cream.

Add the Chocolate: Melt the chocolate chips and dip the tops of the filled éclairs into the melted chocolate. Allow the chocolate to cool and set before enjoying.