1 Beat together butter, sugar and 1 pinch of salt until smooth with a hand mixer. Mix in 1 egg yolk.
2 Add flour and beat just until a smooth dough. Press into a disk, wrap in pastic wrap and refrigerate for 1 hour.
3 Allow dough to sit at room temperature briefly and then roll out on a floured work surface to about 3 mm (approximately 1/3 inch) thick.
4 Using a flour-dusted plate as a guide, cut out 6 rounds, about 12 cm (approximately 5 inches) in diameter. Knead together scraps, roll out again and cut out more rounds.
5 Butter 6 tartlet molds (10 cm or approximately 4 inches in diameter) and line with dough rounds, pressing firmly with a fork. Trim excess dough.
6 Place parchment paper circles cut to fit on top of dough rounds and fill with dried beans. Bake on second rack from bottom of preheated oven at 200°C (fan 165°C) (approximately 400°F) for about 15 minutes.
7 Let cool on a wire rack and remove from molds.
8 Rinse lemons in hot water, wipe dry and finely grate zest from 2 lemons.
9 Squeeze juice from lemons. Mix 160 ml (approximately 3/4 cup) juice with lemon zest, sugar and butter in a metal bowl.
10 Place metal bowl over a pot of simmering water until butter melts. Add remaining egg yolk and the egg with 2-3 tablespoons more lemon juice and beat over the water bath until thick and creamy, 8-10 minutes.
11 Pour custard through a fine sieve into prepared tartlet shells. Let cool completely before serving.