In a food processor, place the flour, salt, and sugar and process until combined.  Add the butter and process until the mixture resembles coarse meal (about 15 seconds).  Pour 1/4 cup (60 ml) water in a slow, steady stream, through the feed tube until the dough just holds together when pinched.  Add remaining water, if necessary.  Do not process more than 30 seconds.

Turn the dough out onto your work surface and gather it into a ball.  Divide the dough into two equal pieces, flatten each portion into a disk, cover with plastic wrap, and refrigerate for 30 minutes to one hour before using.  This will chill  the butter and allow the gluten in the flour to relax.   At this point you can also freeze the dough for later use.  

For each disk of pastry, on a lightly floured surface, roll out the chilled pastry to fit it into a 8 or 9 inch (20 to 23 cm) tart pan.   To prevent the pastry from sticking to the counter and to ensure uniform thickness, keep lifting up and turning the pastry a quarter turn as you roll (always roll from the center of the pastry outwards to get uniform thickness).    To make sure it is the right size, take your tart pan, flip it over, and place it on the rolled out pastry.  The pastry should be about an inch larger than your pan.

When the pastry is rolled to the desired size, lightly roll the pastry around your rolling pin, dusting off any excess flour as you roll.  Unroll on  the top of your tart pan.  Never pull pastry or you will get shrinkage (shrinkage is caused by too much pulling of the pastry when placing it in the pan).  Gently lay in pan and with a small floured piece of pastry, lightly press pastry into bottom and up sides of pan.  Roll your rolling pin over top of pan to get rid of excess pastry.  With a thumb up movement, again press dough into pan.  Roll rolling pin over top again to get rid of any extra pastry.  Prick bottom of dough (this will prevent the dough from puffing up as it bakes).  Cover and refrigerate for 20 minutes to chill the butter and to rest the gluten.

To prebake the tart shell:  Preheat oven to 400 degrees F (205 degrees C) and place rack in center of oven.  Line the unbaked pastry shell with parchment paper or aluminum foil.  Fill tart pan with pie weights or beans, making sure the weights are to the top of the pan and evenly distributed over the entire surface.  Bake crust for 20 to 25 minutes or until the crust is dry and lightly browned.  Remove weights and cool crust on wire rack.  Proceed with desired recipe that calls for a prebaked shell.

Makes two - 9 inch (23 cm) tart shells.