In a large glass bowl, rub lemon zest with sugar until sugar is fluffy and fragrant of lemon.
Add eggs and lemon juice and whisk until combined.
Place the bowl over a pot of boiling water (making sure the water doesn't touch the bowl) and whisk constantly until the curd reaches 160°F. The texture of the curd should be similar to ketchup as it will thicken as it cools.
Strain the lemon curd into a medium bowl.
Add butter and whisk until the butter has melted and incorporated into the curd.
Wrap the lemon curd with plastic wrap, ensuring that the plastic wrap directly touches the surface of the curd to prevent the curd from forming a skin. Chill until cool.
Scoop 1 tbsp (20 grams) scoops of curd onto a parchment lined baking sheet and chill until frozen solid, for around 2-3 hours.
Lemon Cookies
Preheat the oven to 350°F and line a baking sheet with parchment paper.
In a large bowl, combine flour, baking soda and salt. Set aside.
In another large bowl, rub granulated sugar and lemon zest until the sugar is fluffy and fragrant.
Add the icing sugar and butter, then cream until light and fluffy.
Add the egg and lemon juice and mix until smooth.
Add the flour mixture and mix until just combined.
Chill the dough for 15 minutes to make the dough easier to handle.
Scoop the dough into 4 tbsp balls and wrap the dough around each ball of frozen lemon curd.
Transfer the cookies to the prepared baking sheet, leaving 3 inches (8cm) between each cookie.
Bake for 12-14 minutes or until the center of the cookies become matte and dry rather than wet and shiny.
Notes
Please note you may have a couple tablespoons of extra lemon curd left. You can defrost the frozen balls of lemon curd and then spread them on toast or your morning muffin to use them up!