Place the water, milk, sugar, salt, and butter in a sauce pot and it bring to a boil. Add the flour and mix vigorously. Then turn down the heat to dry out the mixture until the dough stops sticking to the sides of the pot. Place the dough into a mixer that is fitted with a paddle attachment and mix for 2 to 3 minutes to cool slightly. Add the eggs one at a time, making sure they are incorporated well before adding the next egg. With a plain tip, pipe the dough into éclairs on sheet pans that are lined with parchment paper. Bake at 400ºF/205ºC with the vent open until golden brown and fully dried.
In a stand mixer combine the pastry cream and milk, whip on high speed for 5 minutes. Fold in the pistachio paste into the pastry cream. Fold the whipped cream into the pastry cream mixture.
