In 9-inch cast-iron skillet over medium-high heat cook 2/3 cup sugar until golden brown, about 5 minutes, swirling pan occasionally. Place skillet on ice to stop browning. Dot bottom of skillet with 2 tablespoons butter, cut into small pieces. Toss apples with 3 tablespoons sugar and cinnamon. Arranged apples tightly together around edge of skillet, rounded side-down. Fill in center in concentric circle. Add second layer of apples, filling in separations. Apples should be tightly packed. Dot surface with remaining butter, cut into small bits. Place pastry on top of apples. Tuck pastry edges down around sides of pan and apples. Place skillet on baking sheet to catch juices. Bake at 400 degrees until crust 4 browned and juices are thickened, about 1 hour and 10 minutes. Let stand 10 minutes. Place platter over skillet. Gently invert tart onto platter. Can be made few hours ahead and kept at room temperature. Tart can be reheated on serving platter at 250 degrees until} barely warm, about 7 minutes. Serve with vanilla ice cream. Makes 6 servings. Each serving contains about: 621 calories; 256 mg sodium.; 16 mg cholesterol; 29 grams fat; 89 carb