Choux Pastry: Preheat oven to 400 degrees F (200 degrees C) and place rack in center of oven. Line a baking sheet with parchment paper or lightly butter or spray the pan with a non stick vegetable spray.
In a bowl, sift or whisk together the flour, sugar and salt.
Place the butter and water in a heavy saucepan over medium high heat and bring to a boil. (Make sure that the butter melts before the water boils to reduce the amount of evaporation.) Remove from heat and, with a wooden spoon, add the flour mixture, all at once, and stir until combined. Return saucepan to the heat and stir constantly until the dough comes away from the sides of the pan and forms a thick smooth ball (about 1-2 minutes). Transfer the dough to your electric mixer, or use a hand mixer, and beat on low speed to release the steam from the dough (about a minute). Once the dough is lukewarm start adding the lightly beaten eggs (dough will separate and then come together) and continue to mix until you have a smooth, thick paste (dough will fall from a spoon in a thick ribbon). Spoon or pipe 12 small mounds of dough onto the baking sheet, spacing about 2 inches (5 cm) apart. With a pastry brush, gently brush the tops of the dough with a lightly beaten egg.
Bake for 15 minutes and then reduce the oven temperature to 350 degrees F (180 degrees C). Continue to bake for a further 30 to 35 minutes or until the shells are a nice amber color and when split, are almost dry inside. Turn the oven off, poke a couple of holes in each puff and, with the oven door slightly ajar, let the shells completely cool (and dry out).
Whipped Cream: In a large mixing bowl, place the whipping cream, vanilla extract, and sugar and stir to combine. Cover and chill the bowl and whisk in the refrigerator for at least 15 minutes. When chilled, whip the cream just until stiff peaks form.
To Assemble: Split the pastry shells in half and fill (or pipe) with whipped cream. Place the top half of the pastry shell on the whipped cream and dust with powdered (confectioners or icing) sugar. Leftover Cream Puffs can be stored in the refrigerator.