Sift together flour, salt and sugar. Place water and butter in a heavy pan and bring to a boil. Add flour in one fell swoop and stir quickly with a wooden spoon. It looks rough at first, but suddenly becomes smooth, at which point you stir faster. In a few minutes, the paste becomes dry, does not cling to the spoon or edges of the pan and when the spoon is pressed on it lightly, it leaves a smooth imprint. Do not overcook. Remove pan from heat. After 2 minutes, add one egg at a time, beating vigorously after each addition. Continue to beat until dough no longer looks slippery. Drop from spoon onto baking sheet forming small globules of dough. Bake in preheated, 400 degrees oven for 10 minutes. Reduce heat to 350 degrees and bake for about 25 minutes longer. Do not remove them from the oven until they are quite firm to the touch. Cool the shells away from any draft. Cut them horizontally and fill with your favorite pudding. Sprinkle powdered sugar on top.