In a medium saucepan, heat the milk to a boil over medium heat. In another bowl, whisk the egg yolks and cornstarch with sugar until no lumps remain. Whisk in 1/4 cup of the hot milk mixture until incorporated, then add back to saucepan. Cook over medium heat, whisking constantly, until thickened. In a small microwave safe bowl, microwave chocolate wafers for 1 minute until melted. Stir into saucepan until fully combined. Cover with plastic wrap, pressing the plastic against the surface of the custard. Chill at least 2 hours.

Preheat the oven to 425 degrees. Line a baking sheet with parchment paper. In a large saucepan, bring the water, butter, salt and sugar to boil over medium-high heat. Add in flour and stir with a wooden spoon, using force, slapping spoon against dough. Mix for about 90 seconds until combined and dough no longer sticks to the man. Add dough to a stand mixer with paddle attachment. Mix at medium speed to release some steam, then with mixer running, add 4 eggs, 1 egg at a time. Mix until the dough is smooth.

Using a pastry bag fitted with a large star tip, pipe 12 eclairs onto the lined baking sheet, leaving 2 inches of space between them. Bake at 425 for 15 minutes, then reduce the heat to 375 degrees and bake until puffed up lightly brown, about 20 minutes more. Let cool completely.

With a serrated knife, slice cooled eclairs lengthwise. 

Heat 5 oz of heavy cream in a microwave for about 2 minutes until hot, but not scaling. Add finely chopped ruby chocolate to bowl. Let sit for 2-3 minutes then stir to combine. 

Dip top half of pastry in ganache and sprinkle crushed, freeze dried raspberries on top. Pipe chocolate pastry cream into bottom and sandwich together.