For the Crust. In the work bowl of a food processor, place flour, confectioners’ sugar, and salt; pulse until combined. Add cold butter, and pulse until mixture is crumbly. With processor running, add egg yolk and 2 tablespoons (30 grams) ice water, pulsing until dough comes together. Shape dough into a disk, and wrap in plastic wrap. Refrigerate for at least 30 minutes or up to 24 hours.
Preheat oven to 350°F (180°C).
On a lightly floured surface, roll Tart Dough into a 12-inch circle. Transfer to a 9-inch round tart pan, pressing into bottom and up sides. Trim excess dough. Using a fork, prick bottom of tart shell. Freeze for 15 minutes. Top dough with a piece of parchment paper, letting ends extend over edges of pan. Add pie weights (or uncooked rice or dried beans).
Bake until edges are set, about 20 minutes. Carefully remove paper and weights. Bake until crust is golden brown, about 10 minutes more. Let cool completely on a wire rack.
For the Ganache. Place chocolate in a medium heatproof bowl.In a medium saucepan, heat cream and butter over medium heat, stirring frequently, just until bubbles form around edges of pan (do not boil). Remove from heat, and pour over chocolate. Let stand for 5 minutes; stir until chocolate is melted and mixture is smooth. Pour two-thirds of Chocolate Ganache into prepared crust, and spread to edges. Freeze for 45 minutes.
Set aside the remainder of the ganache to splash all over the tart.
For the Curd. In the top of a double boiler, whisk together sugar, eggs, butter, and lemon zest and juice. Cook over simmering water, stirring constantly, until thickened, about 10 minutes. If your temperature is on the lower side, this will take longer. Strain mixture (don't skip), discarding solids. Cover and refrigerate for 30 minutes.
Pour lemon curd over Chocolate Ganache in pan. Refrigerate until set, about 2 hours. Just before serving, drizzle with remaining Chocolate Ganache. (See my note above in the 'Before We Get Started' section on how to soften up the ganache again.)