In a food processor or a bowl, whirl or stir flour and sugar to blend. Add butter, and whirl or rub in with your fingers until fine crumbs form. Add egg yolk; whirl until dough is blended and comes together, or mix with a fork until blended, then press into a ball. Press pastry evenly over bottom and up sides of a 10 1/2-inch tart pan with removable rim. Bake in a 350° regular or convection oven until golden, 15 to 20 minutes.