In a saucepan, combine water, butter, sugar, and salt and bring to a boil. Remove the pan from the heat and mix the flour into the liquid. Stir the mixture into a paste. Return the pan to a medium heat. Stir the mixture until it pulls away from the sides of the pan and is slightly shiny, about 3 minutes.
Transfer the paste to a bowl, and beat until slightly lukewarm. Add three eggs and mix them in thoroughly. Before adding the last egg, beat it in a small bowl and add it by tablespoons until the batter is smooth and tight, you will not need the full egg.
Heat the oven to 400°F
Spoon or pipe the dough onto a non stick or parchment lined pan making each puff 2-3 inches in diameter 1/8 in height.
Bake in the middle of the oven for 15 minutes then turn the oven down to 350°F for 30 minutes, until the puffs have a nice golden brown color
Turn off the oven and remove the pan. Poke a hole in the bottom or side of each puff to let moisture escape then return the tray back to the still warm oven and let them sit until cool.
Slice off the top third of each puff and you should see hollow voids.
Fill as you desire.
I used homemade custard, homemade whipped cream and strawberries, but use what you like.