Fill a large pot with water. Place on the cook top and bring the water temperature to 180°F | 82°C.
Zest the lemons, removing only the yellow skin and not any of the pith (white part that is bitter). Place the zest into a food processor and add the sugar. Pulse several times to breakdown the peel, into the sugar, as the essential oils will be released into the sugar.
Add the room temperature butter to the food processor and cream the butter with the lemon sugar. scrape down the sides of the bowl, to make sure all the butter and sugar are fully incorporated and creamy.
Then, with the motor running, add one egg at a time through the top feed tube, mixing until smooth, before adding the next egg.
Next, add the lemon juice in a slow stream, blending into the butter | egg mixture. Finally add the salt and mix well.
Have a large bowl of ice, with a just enough water to loosen the ice that a bowl can sit into it, making an ice bath.
Pour the mixture into a metal bowl, large enough to hold the the pre-curd, with extra room to stir | whisk. Place the bowl over the water bath and stir. bringing the temperature of the Lemon Curd to 170°F | 77°C. The eggs will set and the curd will thicken between 170°F | 77°C - 175°F | 79°C. Keep stirring and once the curd is thick, remove it from the hot water bath and place it into the ice bath; this will stop the cooking and chill final curd faster.
Transfer the final Lemon Curd to a container and store in the refrigerator for up to 2 weeks.