Oranges, underneath the signature caramelized topping, add a surprising element to this classic dessert.
Make the crusts: Pulse flour, sugar, and 1/2 teaspoon salt in a food processor until combined. Add butter, and pulse until mixture resembles coarse crumbs with some larger pieces remaining, about 10 seconds. Whisk together egg, yolk, and water. With machine running, quickly add egg mixture. Pulse until mixture just begins to hold together. Press dough into a disk, and wrap in plastic. Refrigerate until firm, about 30 minutes.
Set six 4-inch tart rings on a parchment-lined baking sheet. Roll out dough to a 1/8-inch thickness on a lightly floured surface. Cut out six 6-inch circles, rerolling scraps as needed. Press dough into bottoms and up sides of tart rings, patching any holes or tears, leaving an overhang at the top of each. Prick bottoms of tart shells all over with a fork, and freeze until firm, about 1 hour. Meanwhile, preheat oven to 350 degrees. Trim excess dough flush with edges of rings using a knife.
Bake, pressing down dough if puffing, until lightly golden, about 15 minutes. Let cool. Reduce oven temperature to 325 degrees.
Make orange caramelized almonds: Remove zest from orange in strips using a vegetable peeler; reserve for filling. Cut away pith; slice fruit along membranes to release segments into a bowl. Squeeze juice from membranes into bowl; discard. Reserve half the segments for another use; coarsely chop remaining segments.
Heat sugar and water in a saucepan over high heat, stirring constantly, until sugar dissolves. Bring to a boil, washing down sides of pan. Cook, swirling often, until sugar is pale amber and starts to caramelize. Add almonds, and stir to toast. Cook until medium to dark amber in color. Add orange and juice and a pinch of salt. Remove from heat, and stir until smooth.
Make the filling: Bring cream and reserved orange zest to a boil in a medium saucepan. Remove from heat; cover, and let stand for 2 hours. Spread 1 tablespoon orange caramelized almonds in a flat, even layer onto bottom of each tart shell (you will have more almonds than needed to cover the tart shell bottoms; reserve remaining almonds for another use). Freeze tart shells until caramel is firm, about 20 minutes.
Bring cream to just under a boil. Meanwhile, whisk together yolks, sugar, and a pinch of salt. Slowly whisk cream into egg mixture. Strain through a fine sieve; discard zest.
Divide cream mixture evenly among tart shells, filling each to the top. Bake, rotating sheets halfway through, until just set, about 20 minutes. Let cool, then refrigerate for 1 hour to set.
Sprinkle tops with sugar. Hold a small handheld kitchen torch at a 90-degree angle 3 to 4 inches from surface of each tart, and move flame back and forth until sugar is caramelized and deep golden brown, or broil until sugar is caramelized. Serve immediately.
Make ahead: Dough can befrozen for up to 1 month. Thawbefore using.