Combine flour and salt.
Cut in butter until mixture resembles coarse crumbs. Do not over mix.
Gradually sprinkle in water, stirring gently. Add only enough water to moisten and bind the dough.
Form into disc, wrap in plastic wrap and refrigerate for 30 minutes before rolling.
Roll out dough into a 12-inch round; fit it into a 10-inch tart pan with removable rim, trimming away excess. For best results freeze tart shell before filling.
Preheat oven to 400°F.
Arrange sliced apples tightly together with core-side down in the pastry shell.
Thoroughly combine sugar and cornstarch. Sprinkle sugar mixture over the apples and top with thin slices of butter.
Place tart pan on rimmed baking sheet.
Bake for 45- 50 minutes or until the apple slices have browned edges and the crust is completely baked.
Warm apple jelly to liquefy and then brush it over the tart while it is still hot.