Heat oven to 350°F. In large bowl, mix flour, 2 tablespoons sugar, the salt and lemon peel. With pastry blender or fork, cut in butter and shortening until mixture resembles coarse crumbs. Stir in egg yolks and 1/2 cup of the milk. With fork, stir until mixture leaves sides of bowl and forms a ball, adding milk 1 tablespoon at a time as necessary. Form dough into 2 balls.