In a Medium saucepan, combine 1/2 cup water, 1/2 cup milk, 8 Tbsp butter, 1 tsp sugar and 1/4 tsp salt. Bring to a boil over medium heat then remove from heat and stir in 1 cup flour all at once with a wooden spoon.

One flour is incorporated, place back over medium heat about 1 1/2 to 2 minutes stirring constantly (to release extra moisture and partially cook flour), or until dough comes together into a smooth ball and a thin film forms on bottom of pan.

Transfer to a large mixing bowl and beat using an electric hand mixer on medium speed for 1 minute to cool the mixture slightly. Add 4 eggs, 1 at a time, allowing each egg to fully incorporate between additions. Beat until dough is smooth and forms a thick ribbon when pulled up. 

Pipe eclairs over baking sheet lined with silicone using a 1/2” round tip. Pipe 18-20 (4” long and 3/4” wide) strips, keeping them 1 1/2" apart.

Bake at 425˚F for 10 minutes. Without opening oven, reduce temp to 325˚F and, bake 30 minutes longer or until golden brown. Transfer to wire rack to cool while making pastry cream.

In a medium saucepan bring 2 cups milk, vanilla bean and scraped seeds just to a boil, stirring to prevent film from forming.

In a separate large bowl, whisk together 3/4 cup sugar, 1/4 cup corn starch and pinch of salt. Add 4 egg yolks and whisk until smooth, creamy and lightened in color - it takes a couple of minutes but it will get there. 

Gradually (so the eggs don't curdle), while whisking constantly, add hot milk in a steady stream until all of it is incorporated. Pour mixture back into saucepan and bring to a boil while whisking constantly then whisk another 30 seconds until mixture is thick and pudding-like in consistency.

Transfer pastry cream to a medium bowl (whisk in 2 tsp vanilla extract if using). Cut butter into pieces and quickly whisk into the custard until fully incorporated Cover with plastic directly over the surface of the cream, let it cool slightly then refrigerate 30 minutes or until cool. 

With a small pastry tip, poke 2-3 holes through the bottom of each cooled pastry. Pipe cream inside, scraping off excess. Refrigerate eclairs while making chocolate glaze.

Place 4 oz of chocolate chips into a small heat-safe bowl. 

Heat 1/2 cup heavy whipping cream (in a saucepan or microwave) until it is just at a simmer then remove from heat and pour over chocolate chips. Let rest 2 minutes then whisk from the center outwards until smooth sauce forms. 

Dip the top half of filled and chilled eclairs into the chocolate sauce, allowing excess to drip off.