For apples, preheat oven to 400 degrees. Scatter butter pieces and sprinkle sugar evenly in a 9 to 10-inch copper tartin pan or heavy baking pan. Tightly pack apple halves around inside edge of pan, reserve 4, standing upright, nestled against one another, with round side tilted down. Place 4 remaining halves in similar position in center of pan. (Apples will shrink as they cook and slip round side down into pan.) Bake for about 2 hours. Transfer pan from oven to stove top and cook over medium-high heat until butter and sugar caramelize to a rich brown, 15 to 20 minutes. Remove from heat, and gently ease sticky apples away from side of pan with a knife. Refrigerate overnight so that apples firm up and "confit" further.
For pastry, preheat oven to 350 degrees about 1 hour before serving tart. Sift flour, salt, and sugar into a bowl. Rub butter into flour mixture with your fingers until it resembles coarse crumbs. Sprinkle in 3 tablespoons ice water and work dough until it just holds together. Form into a ball, wrap in plastic, and refrigerate for 30 minutes. Roll out dough on a floured surface into a 12-inch circle. Drape pastry over apples and pan. Roll the rolling pin across of pan to cut off excess pastry and allow pastry to fall over apples against the inside edge of pan. Bake in oven (still at 350) until pastry is flaky and golden, about 20 minutes. Remove from oven, place a flat ovenproof platter on top of tartin pan and invert quickly and carefully. Do not unmold yet. Reduce heat to 300 degrees and return platter and pan to oven for 10 minutes. Remove tartin pan and serve warm.
Recipe courtesy of Coleman Andrews, Saveur Cooks French