1-Preparing the Tartlet Shells: First, combine 250 grams of all-purpose flour, 50 grams of sifted icing sugar, and a pinch of fine salt in a food processor. Add 120 grams of cold unsalted butter cut into small cubes; pulse until small crumbs form. Whisk 1 large egg separately, then add it to the mixture and pulse slowly until dough forms, then gather it into a ball.

2-Preparing the Tartlet Shells: Roll the dough between two sheets of baking paper to about 4 mm thickness and chill it in the refrigerator for at least 1 hour, up to 24 hours. Cut out pastry rounds using a cookie cutter that’s 1.5 to 2 cm wider than your muffin pan openings, then gently press the disks into the pan, removing any air bubbles. Chill again for at least 2 hours, preferably overnight.

3-Preparing the Tartlet Shells: Preheat your oven to 160°C/325°F and prick the base of each shell with a fork. Place the pan in the freezer while the oven heats, then line each shell with baking paper and fill with baking beads or rice. Bake for 15 minutes, remove the weights and paper, and bake for another 15 minutes until golden and dry. Let them cool completely before proceeding.

4-Making the Lemon Curd: In a small pot, whisk together 4 egg yolks, 100 grams of caster sugar, and 125 ml of lemon juice. Cook over very low heat, whisking constantly, until the mixture thickens, about 3-5 minutes. Gradually add 75 grams of cubed unsalted butter, whisking until melted before adding more, and stir in 1 lemon zest if using.

5-Making the Lemon Curd: Continue cooking on low heat for 5 to 15 minutes, whisking constantly, until the curd thickens enough that a line drawn on the back of a spoon stays clear. This step ensures a silky filling that’s full of flavor.

6-Assembling and Final Steps: Pour the warm lemon curd into the cooled tartlet shells and tap the pan gently to remove air bubbles. Chill in the refrigerator for at least 2 to 3 hours to set. The total preparation time includes 45 minutes of prep, 30 minutes of cooking, and 6 hours of resting, making the whole process around 7 hours and 15 minutes.