Make the Tart Shells:

1. In a food processor, pulse the flour, butter, and sugar together until the mixture resembles coarse crumbs.
2. Add the egg yolk and pulse again. Slowly add the ice water, 1 tablespoon at a time, until the dough comes together.
3. Form the dough into a disk, wrap it in plastic wrap, and chill in the refrigerator for 30 minutes.
4. Preheat the oven to 375°F (190°C). Roll out the chilled dough on a lightly floured surface to about 1/8-inch thick.
5. Cut out circles to fit your tartlet pans (2–3 inches in diameter), and press the dough into the pans. Trim any excess dough. Prick the bottoms with a fork.
6. Line each shell with parchment paper and fill with pie weights or dried beans. Bake for 10 minutes, then remove the weights and bake for another 5–7 minutes, until lightly golden. Let cool completely.

Make the Lemon Curd:

1. In a heatproof bowl, whisk together the eggs, sugar, and lemon juice.
2. Place the bowl over a pot of simmering water (double boiler) and cook, whisking constantly, until the mixture thickens (about 10–12 minutes).
3. Remove from heat and stir in the butter and lemon zest until smooth. Let the curd cool slightly before filling the tart shells.

Assemble the Tartlets:

1. Spoon or pipe the lemon curd into the cooled tart shells, smoothing the tops with a spatula.
2. Optional: Garnish with fresh berries, powdered sugar, or a dollop of whipped cream.