Preparation Preheat oven to 350°F with rack in middle. Roll out dough into a 13-inch round on a lightly floured surface with a lightly floured rolling pin. Transfer to an ungreased 17- by 14-inch baking sheet. Sprinkle semolina over dough, leaving a 2-inch border all around. Toss apples with lemon juice and zest in a large bowl, then mound on top of semolina (leaving border) and sprinkle granulated sugar over apples. Fold in dough border over apples, pleating dough as necessary, to form a 9-inch round. Bake galette 30 minutes, then loosely cover with foil and bake until apples are tender and crust is golden, 25 to 30 minutes more. Remove galette from oven and turn on broiler. Dust apples with confectioners sugar and broil 5 to 6 inches from heat until apples are just golden, 1 to 3 minutes (watch carefully; sugar burns easily). Slide galette from baking sheet onto a rack, then cool to warm or room temperature. Cooks' note:Galette can be baked 5 hours ahead and cooled, uncovered, then kept at room temperature. If desired, reheat in a 350°F oven until warm, about 5 minutes.