Fresh Orange Tart with Hazelnut Crust

Ingredients
Orange filling: Crust:
 * 1 1/4 teaspoons unflavored gelatin
 * 1 tablespoon water
 * 1 cup Sugar
 * 2 tablespoons plus 2 teaspoons finely grated orange peel
 * 2 teaspoons finely grated lemon peel
 * 4 large eggs
 * 3/4 cup fresh orange juice
 * 3 tablespoons fresh lemon juice
 * 1 cup plus 6 tablespoons (2 3/4 sticks) unsalted butter, cut into tablespoon-size pieces, room temperature
 * 1 1/4 cups all purpose flour
 * 1/2 cup powdered sugar
 * 1/4 cup hazelnuts
 * 1/4 teaspoon salt
 * 9 tablespoons chilled unsalted butter, cut into 1/2-inch cubes
 * 1 large egg yolk

Directions
For orange filling:
 * 1) Sprinkle gelatin over 1 tablespoon water in small bowl.
 * 2) Let stand 10 minutes to soften. Combine Sugar, 2 tablespoons orange peel, and lemon peel in medium metal bowl.
 * 3) Using fingertips, rub ingredients together until Sugar is moistened.
 * 4) Add eggs; whisk until smooth. Whisk in both juices.
 * 5) Place bowl over saucepan of simmering water (do not allow bottom of bowl to touch water);
 * 6) Whisk constantly until mixture thickens and thermometer inserted into mixture registers 180 °F, about 5 minutes. Remove from heat.
 * 7) Add gelatin mixture and stir until dissolved.
 * 8) Strain orange mixture into blender; let cool until thermometer inserted into mixture registers 140 °F, about 10 minutes.
 * 9) With blender running, add room-temperature butter 2 pieces at a time and process until blended.
 * 10) Continue blending 3 minutes longer.
 * 11) Transfer filling to bowl; mix in remaining 2 teaspoons orange peel.
 * 12) Cover and chill overnight.
 * 13) For crust:
 * 14) Butter 9-inch square tart pan with removable bottom.
 * 15) Finely grind flour, Sugar, nuts, and salt in processor.
 * 16) Add butter and cut in using on/off turns until mixture resembles coarse meal.
 * 17) Add egg yolk and blend in using on/off turns just until moist clumps form (do not allow dough to form ball). Press dough onto bottom and up sides of prepared pan (crust will be about 1/4 inch thick).
 * 18) Using thumb, press around sides to extend crust 1/4 inch above edge of pan. Chill 1 hour.
 * 19) Preheat oven to 375 °F. Bake crust until golden brown, about 20 minutes.
 * 20) Cool crust completely on rack. (Crust can be made 1 day ahead.
 * 21) Store airtight at room temperature.)
 * 22) Stir orange filling to loosen.
 * 23) Spoon enough chilled orange filling into crust to fill completely.
 * 24) Chill tart at least 1 hour and up to 4 hours.
 * 25) Garnish with candied blood orange slices.
 * 26) Drizzle oranges with some of syrup. Serve cold.