01 - Preheat oven to 350°F. Lightly grease a 12-cup mini tartlet or muffin pan.
02 - In a bowl, combine flour, powdered sugar, and salt. Add cold butter and work in with fingertips or a pastry cutter until mixture resembles coarse crumbs.
03 - Add egg yolk and 1 tablespoon cold water. Stir until dough just comes together, adding more water if needed.
04 - Divide dough into 12 portions. Press each evenly into the base and up the sides of the tartlet molds. Prick bases with a fork.
05 - Bake shells for 15 to 18 minutes, or until golden. Cool in pan for 5 minutes, then transfer to a rack to cool completely.
06 - Whisk eggs and sugar together in a heatproof bowl. Add lemon juice and zest.
07 - Place bowl over a saucepan of gently simmering water. Cook, whisking constantly, until mixture thickens and coats the back of a spoon, about 8 to 10 minutes.
08 - Remove from heat and whisk in butter gradually until smooth.
09 - Pour lemon curd into cooled tartlet shells. Chill for at least 1 hour to set.
10 - Optionally, decorate with whipped cream, fresh berries, or a dusting of powdered sugar before serving.