Make the tart dough by pulsing flour, sugar, and salt in a food processor. Add cold butter cubes and pulse until the mixture resembles coarse crumbs with pea-sized pieces.
Add the egg yolk and 2 tablespoons ice water, pulsing until the dough just starts to come together. Add the remaining tablespoon of water only if the dough seems too dry.
Turn the dough onto a lightly floured surface, shape it into a disk, wrap tightly in plastic wrap, and refrigerate for at least 1 hour or up to 2 days.
Roll the chilled dough on a floured surface into an 11-inch circle about 1/8-inch thick. Carefully transfer it to a 9-inch tart pan with a removable bottom, pressing gently into the corners without stretching.
Trim excess dough by rolling your pin across the top edge, then prick the bottom all over with a fork. Refrigerate for 30 minutes while you preheat the oven to 375°F.
Line the chilled tart shell with parchment paper and fill with pie weights or dried beans. Bake for 20 minutes, then remove the weights and parchment and bake for another 10-12 minutes until golden brown. Cool completely.
Prepare the lemon curd by whisking eggs, sugar, lemon juice, zest, and salt in a medium saucepan until smooth and well combined.
Cook the mixture over medium-low heat, stirring constantly with a wooden spoon or silicone spatula, until it thickens enough to coat the back of the spoon, about 8-10 minutes. Do not let it boil.
Remove from heat and immediately stir in the butter cubes until completely melted and smooth. Strain the curd through a fine-mesh sieve into a bowl to remove any lumps.
Pour the warm lemon curd into the cooled tart shell, smoothing the top with an offset spatula. Refrigerate uncovered for at least 3 hours or until fully set before slicing and serving.
