Preheat your oven to 350 F or 175 C. Line a baking sheet or tray with parchment paper or a silicone mat.
Place water, butter, sugar (and salt, if using) in a saucepan and heat on medium hear until it just begins to boil. Remove from heat immediately. If using vanilla, add it now and stir.
Add the flour all at once. Using a firm utensil (like a wooden spoon), mix until everything is combined and place the pot back on medium heat.
Keep stirring for about 2 minutes until a cohesive dough forms and the raw flour taste cooks off.
Leave the dough to cool for about 10 minutes. You can also move the dough to a separate bowl to cool faster.
Whisk the egg in a separate bowl. Then, add it to the dough. Mix vigorously until a smooth and pipeable dough/thick batter forms. If still too dry, whisk another egg in the separate bowl and add it a little at a time until it reaches a smooth, pipeable thick batter.Note: It may look like the dough has separated - this is absolutely normal. As you continue to mix, it will come together. See Notes for Tests on the right consistency.
Fill a piping bag or quart-sized Ziploc bag and snip the edge to about 1/2 an inch or 1.3 cm wide. Pipe small mounds of about a tablespoon each onto your baking sheet, leaving a bit of room between each Chouquette. Sprinkle pearl sugar generously over each one.
You should have 10-12 or so Chouquettes.
Bake the Chouquettes for 25 minutes. Do NOT open the door. After 25 minutes, open the oven door for a second to allow steam to escape, then close and bake for another 8-12 minutes until golden.
Remove from the oven and let cool completely on the baking sheet or wire rack. Bon Appétit!
Optional: Poke a small hole at the bottom to release some steam.