Mix flour, salt, and sugar in medium bowl or food
     processor.  Mix in the butter, either cutting in with 
     pastry blender or 2 knives, mixing in with hands, or
     processing for 10 to 20 seconds.  Mixture should 
     resemble fine crumbs when done; it should not be
     a homogeneous, smooth dough.

     Add egg yolk and mix in lightly with fork or process
     for 10 seconds.  Dribble on cold water and vanilla,
     again mixing lightly with fork to distribute evenly or 
     processing for a few seconds. 

     Form dough into ball by pressing together between 
     hands.  If air is very dry and dough crumbles when
     you try to press it into a ball, a little more water may
     be necessary, but be careful not to add too much 
     or dough will be too sticky to roll out.

     Roll out dough on flour-dusted pastry cloth, and fit 
     into 9" pie pan.

     When you bake this dough, you should cover the 
     edge with a strip of aluminum foil, as it burns easily.

     Makes one 9" pie crust.