In a medium sized saucepan, combine the 1/2 cup unsalted butter, 1 cup water and 1/4 teaspoon salt over medium-high heat. Continue to heat over medium-high heat until boiling.
Once boiling, reduce heat to low and stir in 1 cup all-purpose flour with a wooden spoon. Continue to stir over low heat until a ball of dough is formed.
Remove from heat and beat in the 4 large eggs, one at a time. Continue to beat the dough strongly after each egg is added. The dough should begin to become smooth.
Line a baking sheet with parchment paper or a silicone baking mat. Scoop the dough using a cookie scoop (about 1 1/2 tablespoons each) onto the lined baking sheet, leaving enough space between each scoop of dough so they do not touch. Repeat with the rest of the pastry dough.
Bake at 400°F for 35 minutes, or until the pastries have "puffed up" and are golden brown (do not overbake).
Once puffs are removed from the oven, gently poke the side of each puff with a sharp knife to release the steam. Cool puffs on the cookie sheets at least 1 hour before filling.
For the whipped cream filling
In a large mixing bowl, beat the cold 2 cups heavy whipping cream, with the 1/4 cup powdered sugar on high speed with an electric mixer until very soft peaks form. Add in the 1/2 teaspoon vanilla extract and continue to beat until the peaks are more firm.
Using a sharp knife, slice each cream puff 1/3 of the way from the top and remove the top. Gently remove any strands of dough inside the puff and discard.
Fill each cream puff with the sweetened whipped cream. Replace the top back on the cream puff and dust with powdered sugar. Repeat with remaining cream puffs. Store cream puffs in an airtight container, refrigerated.
Notes
To make larger cream puffs, use 1/4 cup of dough per cream puff (yield will be 12 cream puffs)
Cream puffs will keep in the refrigerator for up to 72 hours (store in an airtight container).
Alternately, can fill the cream puffs with a pastry cream or ice cream. If using ice cream, store cream puffs in the freezer.