8 tbsp unsalted butter – cold, cut into small cubes
1 large large egg yolk – beaten
2 tbsp ice water
8 medium clementines – zested to yield 2 tbsp zest and juiced to yield 0.875 cup juice
1 medium lemon – juiced (2 tbsp)
0.75 cups granulated sugar
0.125 tsp fine sea salt
3 large large eggs
2 large large egg yolk
6 tbsp unsalted butter – cut into pieces
clementine segments – for serving
1 tbsp confectioners' sugar – for serving
Instructions
Make the dough: In a bowl, whisk the flour, confectioners' sugar, and 0.25 tsp salt. Cut in the 8 tbsp cold butter until the mixture looks like coarse sand with pea-size bits.
Add the 1 large egg yolk and drizzle in 1–2 tbsp ice water, tossing just until the dough clumps when pressed. Gather into a disk, wrap, and chill until firm, about 1 hour.
Roll the dough on a lightly floured surface to an 11-inch round. Fit it into a 9-inch tart pan with a removable bottom, trim edges, and dock the bottom with a fork. Freeze 20 minutes while you heat the oven to 375°F (190°C).
Blind-bake: Line the shell with parchment and fill with pie weights. Bake 18–20 minutes. Remove weights and parchment; bake 10–12 minutes more until golden. Cool on a rack 30 minutes.
Make the filling: Finely zest the clementines to yield 2 tbsp zest, then juice them to yield about 0.875 cup juice. Juice the lemon to get 2 tbsp. In a medium saucepan, whisk the granulated sugar, 0.125 tsp salt, 3 large eggs, and 2 large egg yolks until smooth. Whisk in the combined citrus juices and the zest.
Cook over medium-low heat, stirring constantly with a heatproof spatula, until thickened and just starting to bubble, 8–12 minutes; it should reach 170–175°F and coat the back of a spoon. Immediately strain through a fine-mesh sieve into a bowl, then whisk in the 6 tbsp butter until glossy.
Pour the curd into the cooled tart shell and smooth the top. Chill uncovered until set, 2–3 hours, until the center quivers slightly but does not flow when the pan is nudged.
To serve, garnish with clementine segments or dust with confectioners' sugar as desired. Unmold, slice, and serve chilled.