100 gr Caster Sugar (or fine white granulated sugar)
125 ml Lemon Juice (about 3 large lemons)
75 gr Unsalted Butter (at room temperature)
1 Lemon Zest (optional)
Instructions:
Place the Flour, Icing Sugar and Salt in the bowl of your Food Processor and pulse to mix (see note 1 if making by hands). Add the cold Butter cut into small cubes, then mix to get very small crumbs.
Whisk the egg in a separate bowl and add it to the food processor. Slowly pusle until a dough starts to come together (see note 2).
Bring the dough together into a ball and roll between two sheets of baking paper to be about 4 mm or 1/6 inch thick. Place on a flat tray and leave in the fridge to chill and rest for at least 1 hour, or up to 24 hours.
Remove the baking paper. With a round or fluted cookie cutter that is about 1,5 to 2 cm (0.6 to 0.8 inch) wider than the opening of the muffin pan, cut out disks of pastry (see note 3). Gently slide the disks of pastry into a muffin pan and lightly press on the bottom corners to make sure the pastry is touching the pan all around - and to remove any air bubbles that could be trapped under the pastry. Pro tip: use a muffin pan with perforated bottom to insure an even air flow and optimal baking with minimal shrinkage.
Place back in the fridge to rest and chill for at least 2 hour - preferably overnight.
Preheat your oven on 160'C/325'F. Prick the bottom of the pastries with a fork and place the muffin pan in the freezer while the oven is preheating.
Line each tartlet shells with a small piece of crunched up baking paper and fill with baking beads, rice or beans. Bake for 15 minutes, then remove the weights and baking paper and bake for another 15 minutes, or until golden and dry to the touch. Set aside to cool down completely.
Place the Egg Yolks, Sugar and Lemon Juice in a small pot. Whisk to combine then turn on very low to low heat. Whisk for a few minutes or until the liquid looks like it is starting to thicken - about 3 to 5 minutes.
Cut the butter into small cubes and slowly add them to the pot. Whisk until melted and combined each time before adding more. Add the Lemon Zest
Cook on low heat for 5 to 15 minutes or until the curd has thickened. Continuously whisk to avoid lumps (see note 4).
To check if the curd is cooked, dip the back of a spoon into the curd then draw a line in the curd with your fingers (be careful, it will be hot). Tip the spoon down and check if any of the curd is dripping down over the clear line. If the line stays clear, the curd is ready. If the curd pours over the line, it needs to cook for longer.
While still warm, pour the curd into the tartlet shells. Gently tap each tartlet against a hard surface to remove any air bubbles, then place in the fridge to set for at least 2 to 3 hours (see note 5).