In a food processor or a bowl, combine flour and sugar. Add butter, cut into small pieces; whirl (or rub with your fingers) until fine crumbs form. Add egg yolk; whirl (or mix with a fork) until dough holds together.
Firmly press the dough over bottom and sides of a 10-inch tart pan with removable rim.
Bake in a 300° oven until pale gold, 25 to 30 minutes; let cool. If making ahead, wrap airtight and let stand at room temperature up to 1 day, or freeze to store longer. Thaw unwrapped.