01 - Set the oven to 350°F to prepare for baking the pastry shell.
02 - Pulse flour, powdered sugar, and salt in a food processor. Add cold butter and pulse until the mixture resembles coarse crumbs.
03 - Add egg yolk and pulse briefly. Gradually add ice water, 1 tablespoon at a time, until the dough just comes together.
04 - Press the dough evenly into a 9-inch tart pan and chill in the refrigerator for 20 minutes.
05 - Line the pastry with parchment paper and fill with baking weights. Bake for 15 minutes, then remove weights and bake for an additional 10 minutes until golden. Let cool slightly.
06 - In a heatproof bowl, whisk together sugar, eggs, egg yolks, lemon juice, zest, and a pinch of salt until combined.
07 - Place the bowl over simmering water and whisk continuously until the mixture thickens, about 10 minutes.
08 - Remove from heat and gradually whisk in the cubed butter until the filling is smooth and glossy.
09 - Pour the filling into the prepared tart shell and bake at 325°F for 12 to 15 minutes until just set.
10 - Allow the tart to cool completely, then refrigerate for a minimum of 2 hours before serving.