Heat oven to 400°F. In medium bowl, cut 1/3 cup butter into flour, using pastry blender (or pulling 2 table knives through ingredients in opposite directions), until mixture is crumbly. Stir in egg until dough forms. Press firmly and evenly against bottom and side of ungreased 9-inch tart pan with removable bottom. Bake 12 to 15 minutes or until golden brown; cool on cooling rack.