In a medium-sized, heatproof bowl, combine 55 grams of caster sugar with 4 grams of cornstarch.

Whisk in one egg, followed by 45 grams of fresh lemon juice and the peel from approximately 1/4 lemon.

Place the bowl over a bain-marie, stirring often, and cook for approximately 8 minutes or until the mixture starts to thicken. Continue stirring constantly for an additional 2 minutes until it reaches a thick consistency.

Remove from heat, add 22 grams of unsalted butter, and mix thoroughly to cool the mixture rapidly.

Cover the surface of the curd directly with plastic wrap and refrigerate for a minimum of 30 minutes. This can be prepared a day in advance.

Divide the chilled lemon curd equally into 10 portions on a lined tray and freeze for at least 1 hour or until solid.

In a large bowl, cream together 110 grams of unsalted butter, 110 grams of caster sugar, the zest from 3/4 lemon, and 1 teaspoon of vanilla paste or extract until smooth and well combined.

Incorporate one egg using a whisk.

Sift in 200 grams of all-purpose flour, a pinch of salt, and 1/2 teaspoon of baking soda, gently folding the mixture with a spatula until it forms a soft, non-sticky dough.

Refrigerate the dough for at least 20 minutes, or until it is firm enough to handle, especially in warmer climates.

Using a large ice cream scoop (approximately 5cm or 2 inches in diameter), portion the dough, flatten each piece, and place one scoop of the frozen Lemon Curd Filling in the center. Fold the dough around the filling and roll it into a ball.

Coat each cookie ball in granulated white sugar and place them on a lined baking tray, spaced at least 5cm (2 inches) apart.

Repeat the process until all the dough is used, yielding approximately 9-10 cookies. Work swiftly to prevent the Lemon Curd Filling from melting.

Bake in a preheated fan oven at 180°C (350°F) for 8-9 minutes. The cookies should be very soft in the center with slightly golden edges.

Remove from the oven and allow to cool on the baking tray.