Combine flour, 8 tbsp. butter, and salt in a food processor and pulse until pea-size crumbles form, about 10 pulses. Drizzle in 3 tbsp. ice-cold water and pulse until dough is moistened, about 3—4 pulses. Alternatively, mix flour and salt in a large bowl, and cut in cold butter pieces with a pastry cutter by hand, until pea-size crumbles form. Transfer dough to a work surface and form into a flat disk; wrap in plastic wrap and refrigerate for 1 hour. Unwrap dough and transfer to a lightly floured work surface. Using a rolling pin, flatten dough into a 13″ circle and then transfer to a 11″ tart pan with a removable bottom; trim edges; chill for 1 hour.
Heat oven to 375º. Working with one apple half at a time, thinly slice into sections, keeping slices together. Press sliced apple half gently to fan it out; repeat with remaining apple halves. Place 1 fanned apple half on outer edge of the tart dough, pointing inward; repeat with 7 more apple halves. Separate remaining apple slices. Starting where the apple halves touch and working your way in, layer apples to create a tight rose pattern. Fill in any gaps with remaining apple. Sprinkle with sugar and then dot with remaining butter. Bake until golden brown, 60—70 minutes.
Meanwhile, heat apricot jam in a small saucepan until warmed and loose; pour through a fine strainer into a small bowl and set aside. Transfer tart to a wire rack; using a pastry brush, brush top of tart with jam. Let cool completely.
Recipe from saveur.com