Chop butter, melt in water and just bring to boiling. Immediately add flour, and mix well with wooden spoon, until it forms a dough that leaves the side of the pan (it looks really gross and clumpy at first, but as you keep stirring it fixes itself). Remove from heat and cool 2 minutes.
For a sweet pastry, add the sugar to the beaten eggs. Stir in the eggs, mixing until it look like dough again (this is gross at first too).
Now you have many choices: using a pastry bag or spoon, shape the dough as desired.
Bake at 230C until it looks crisp and golden, about 30 mins for small sized puffs.
Cut in half, or cut a slit in the side to let the steam escape- if you don't do this fairly quickly they get soggy inside.