Preheat oven to 450F, grease a big baking sheet.
In a saucepan combine water and butter, bring to a boil and stir so the butter fully melts. Turn heat down, add flour. When it thickens remove it from the heat.
Mix eggs. Add gradually, mixing well after each pour. Pipe onto baking sheet in 1.5x4" strips. Barely fits on a single big sheet.
Bake 15min at 450F, then turn heat down to 325F for another 20min. Make sure not to open the oven door until near the end of the 20min. They're done when they feel light, airy, and sound hollow when tapped on the bottom. Let them cool on a rack.
After they've cooled, fill with pastry cream. How much cream you need depends on how you're filling them. If you're cutting them in half, you'll need about one recipes worth; if you're injecting them you need more like a recipe and a half.
Then pipe a strip of one recipe worth of chocolate icing along the tops.