Preheat the oven to 425 degrees.
Bring the water to a boil in a medium pot, and melt the butter in it. Add the salt. Dump in the flour all at once, stirring briskly with a wooden spoon. When it is well mixed, remove if from the heat and slowly beat in the eggs until well blended.
Drop by tablespoons (half-teaspoons will give you minature puffs) onto a greased cookie sheet, being careful not to put them too close together. (Lightly greasing the spoons keeps the dough from sticking.)
Bake the puffs for about 18 minutes, then reduce the heat t 350 degrees and continue cooking for about 10 minutes more. Puffs should be golden brown. You can make these up to 8 hours in advance; store in a dry place.
Makes about 3 dozen regular-size puffs or up to 6 dozen mini puffs.
Scald 1 3/4 cups milk to just below the boiling point. Mix the flour with the remaining 1/2 cup milk, and add it to the hot milk, stirring constantly. Add the sugar, salt, and beaten eggs and keep stirring until it thickens, about 10 minutes. Add the vanilla and rum and let cool. (If you are out of rum, use 2 teaspoons vanilla.) If you are making the filling ahead of time, refrigerate.
Pipe the filling into the shells with a pastry bag, or slice the shells in half with a new single-edge razor blade and fill with spoonfuls of cream filling.