Place the gelatin sheet in cold water to soften.
In a medium saucepan, whisk together the eggs and sugar. Slowly whisk in the lemon juice. Put the saucepan over medium heat and whisk constantly until the mixture begins to simmer. Continue simmering for 3-5 minutes until thickened.
Remove the saucepan from the heat and whisk for a few minutes to release the steam and cool the curd slightly. Then, squeeze the water out of the gelatin and then whisk the gelatin into the curd until the gelatin has completely dissolved.
Pour the curd through the strainer into the blender. Turn the blender on low and blend for a few seconds. Add 2-3 pieces of room temperature butter into the blender at a time until the butter is fully incorporated.
Add the lemon zest and blend until combined.
Transfer the lemon curd to an airtight container and allow to cool to room temperature with the lid off. Once cooled, cover the lemon curd with a piece of plastic wrap. Make sure the plastic wrap touches the surface of the curd so a skin does not form. Put the lemon curd in the fridge to cool completely.
This recipe makes approximately 1¾ cups (400g) of lemon curd. It will keep in the fridge for up to 1 week.