Step 1
Preheat the oven to 425 degrees F (220 degrees C). Butter a baking sheet.
Step 2
Heat 3/4 cup plus 1 1/2 tablespoons water 8 1/2 tablespoons butter and salt in a saucepan over medium heat. Bring to a boil; turn off the heat and sift in flour. Beat vigorously with a wooden spoon until mixture is well combined and leaves the sides of the pan.
Step 3
Cool the mixture to room temperature about 10 minutes. Crack in eggs 1 at a time stirring gradually into a smooth dough. Lift the spoon to check the consistency; dough should slide gradually back into the bowl.
Step 4
Fit a piping bag with a coupler and 3/4-inch round nozzle. Drop piping bag nozzle-down into a tall glass and fold edges down around the glass. Spoon dough into the bag. Gather edges and twist together.
Step 5
Pipe dough into 5-inch-long logs onto the prepared baking sheet. Press logs down with wet fingers if any peaks form.
Step 6
Bake in the preheated oven until golden and firm 30 to 35 minutes. Let eclairs cool on a wire rack while preparing the topping and filling.
Step 7
Place chocolate and 1/4 cup butter in the top of a double boiler over simmering water. Stir frequently scraping down the sides with a rubber spatula to avoid scorching until chocolate is melted about 5 minutes. Remove from heat.
Step 8
Beat cream in a chilled glass or metal bowl using an electric mixer until frothy. Add confectioners' sugar and vanilla extract gradually continuing to beat until stiff peaks form. Fill a clean piping bag with the whipped cream.
Step 9
Use a paring knife to cut an X in either end of each eclair. Pipe a portion of the whipped cream into one end of each eclair until it starts to ooze out the other side. Dip the top halves in melted chocolate-butter mixture. Refrigerate eclairs until filling hardens about 30 minutes.