Preheat oven to 375°.
To prepare pastry, lightly spoon flour into a dry measuring cup; level with a knife. Combine the flour, 2 tablespoons sugar, and 1/8 teaspoon salt in a bowl; cut in butter with a pastry blender or 2 knives until mixture resembles coarse meal. Sprinkle surface with ice water, 1 tablespoon at a time; toss with a fork until moist and crumbly (do not form a ball).
Press mixture gently into a 4-inch circle on heavy-duty plastic wrap; cover with additional plastic wrap. Roll dough, still covered, into an 11-inch circle. Place dough in freezer 10 minutes or until plastic wrap can be easily removed. Remove 1 sheet of plastic wrap; let stand 1 minute or until pliable. Fit dough into a 9-inch round removable-bottom tart pan coated with cooking spray. Remove top sheet of plastic wrap. Press dough against bottom and sides of pan. Fold edges under. Pierce bottom and sides of dough with a fork; bake at 375° for 20 minutes. Cool on a wire rack.
To prepare pastry cream, combine 1/2 cup sugar, cornstarch, and 1/4 teaspoon salt in a medium saucepan. Gradually stir in milk; bring to a boil over medium heat. Cook 1 minute, stirring constantly.
Combine egg yolks and egg in a small bowl; stir with a whisk until blended. Gradually stir about one-fourth of hot milk mixture into egg mixture; add to remaining milk mixture, stirring constantly. Cook over medium heat until mixture is thick and creamy, stirring frequently (about 5 minutes). Remove from heat; stir in rind and vanilla. Pour into a bowl; cover surface of pastry cream with plastic wrap. Chill.
Spread half of melted chocolate over the bottom of the crust. Spoon the pastry cream into the crust. Arrange clementine slices over pastry cream. Brush preserves over clementines. Drizzle remaining chocolate over tart. Chill completely; cut into 8 wedges.