Martha used this recipe to make a Lemon-Blueberry Tart on episode 706 of Martha Bakes.
In the bowl of a food processor, combine flour, sugar, and salt. Add butter and yolk and process until mixture resembles a coarse meal, approximately 10 seconds. (To mix by hand, combine dry ingredients in a large mixing bowl; using a pastry blender or two table knives, cut in butter until mixture resembles coarse meal.)
With the machine running, gradually add water through the feed tube. Process just until dough holds together without being wet or sticky; do not process more than 30 seconds. Test the dough at this point by squeezing a small amount together. If it is crumbly, add a bit more water.
Turn dough out onto a large piece of plastic wrap. Grasping the ends of the plastic wrap with your hands, press dough into a flat circle with your fists. This makes rolling easier than if the pastry is chilled as a ball. Wrap dough in plastic and chill for at least an hour.