Make the pastry: In a large mixing bowl, rub the cold butter cubes into the flour, icing sugar, and salt using your fingertips until the mixture resembles fine, pale breadcrumbs. Add the egg yolk and 2 tablespoons of cold water. Bring the dough together with your hands until it forms a smooth, cohesive ball. You should hear no squeak or feel any greasiness. Wrap in cling film and chill for 20 minutes.

Blind bake the shells: Preheat your oven to 180°C (160°C fan). Roll the chilled pastry out on a lightly floured surface to about 3mm thickness. Cut out rounds and press them into a 12-hole tartlet tin. Prick the bases with a fork. Line each shell with a square of baking paper and fill with baking beans or dried rice. Bake for 12 minutes, then remove the paper and beans. The pastry will look set and have a matte, dry appearance.

Finish baking the shells: Return the tins to the oven for another 5-7 minutes, until the pastry is a deep, golden blonde colour and smells nutty and toasted. Remove from the oven and allow them to cool completely in the tin. You'll hear a slight crackle as they cool.

Make the lemon curd: While the shells cool, fill a medium saucepan with a couple of inches of water and bring it to a gentle simmer. In a heatproof bowl (that sits snugly over the pan without touching the water), whisk together the whole eggs, egg yolks, caster sugar, and lemon zest until pale and thick, about 1 minute. The mixture will be light and frothy.

Cook the curd: Pour in the lemon juice and whisk to combine. Place the bowl over the simmering water. Stir continuously with a wooden spoon or a heatproof spatula. After about 8-10 minutes, the mixture will visibly thicken and coat the back of the spoon. You'll see it change from a thin, watery liquid to a thick, opaque custard. The aroma will be intensely lemony.

Finish the curd: Remove the bowl from the heat. Immediately add the cold butter cubes, one at a time, stirring until each piece is fully melted and incorporated. The curd will become glossy and smooth. Strain the curd through a fine-mesh sieve into a clean bowl to remove the zest and any cooked egg bits. Press a piece of cling film directly onto the surface to prevent a skin from forming. Allow it to cool to room temperature. It will have a thick, spreadable, jelly-like consistency.

Assemble the tartlets: Once the pastry shells and the curd are both completely cool, spoon or pipe the lemon curd into each shell, filling them right to the top. The surface should be smooth and shiny. Place the assembled tartlets in the fridge to set for at least 30 minutes before serving.