Whisk together the flour and salt in a mixing bowl. Cut in the cold butter with a knife or pastry blender until the mixture resembles coarse crumbs. (This can also be done in a food processor: pulse the cold butter or shortening until it's the size of small peas. Turn mixture into a bowl and proceed.) Add the ice water a tablespoon at a time, tossing with a fork, until the flour mixture is moistened. Do not add more water than you need: when you squeeze a handful of the moistened pastry mixture, it should form a ball. Wrap in plastic and refrigerate for at least 1 hour or overnight.
Lightly butter 2 pizza pans. Separate 1/3 of the dough; roll into a 6-inch circle on a floured surface. Roll the remaining 2/3 of dough into a 12-inch circle. Place the dough on the prepared pans. Refrigerate for 1 hour.
Preheat an oven to 400 degrees F (200 degrees C). Sprinkle half of the sugar on the dough. Arrange the apple slices in concentric circles over the dough, then sprinkle with the remaining sugar.
Bake in the preheated oven until the crust is golden brown, about 30 minutes.
Meanwhile, place the apricot jam in a blender, and blend until smooth. Pour the jam into a microwave-safe bowl, and heat on high until the jam is warm, about 1 minute. Brush the warm glaze over the apples before serving.