01 - Preheat the oven to 350°F and grease a 12-cup mini tart pan or muffin tin.
02 - In a bowl, combine flour, powdered sugar, and salt. Rub in cold butter with fingertips or a pastry cutter until the mixture resembles breadcrumbs.
03 - Mix in egg yolk and 1 tablespoon cold water. Stir to form a dough, adding more water if necessary. Turn dough onto a floured surface and knead gently until smooth. Wrap in plastic wrap and chill for 15 minutes.
04 - Roll dough out to 1/8 inch thick. Cut into 12 circles large enough to line tartlet molds. Press dough gently into molds and trim excess.
05 - Prick tart bases with a fork. Chill for 10 minutes. Line each shell with parchment and fill with baking beans. Bake for 12 minutes, remove beans and parchment, then bake an additional 5 to 7 minutes until golden. Cool completely.
06 - In a heatproof bowl, whisk eggs, egg yolks, and sugar until combined. Stir in lemon juice and zest.
07 - Place bowl over a pot of gently simmering water (double boiler). Cook, stirring constantly, until thickened and coating the back of a spoon, about 8 to 10 minutes.
08 - Remove from heat and stir in cubed butter until smooth.
09 - Spoon or pipe lemon curd into cooled pastry shells. Chill for at least 1 hour before serving.