Fill a heavy-duty pot or heat-proof container with warm tap water. Attach the immersion cooker and set the temperature to 73.9ºC/165ºF. Cover to speed up heating.
Make the curd:
Combine all the ingredients, except the zest, using a hand whisk, immersion blender or blender. Pour the mixture into a sous vide safe bag or jars, add the zest and seal partially and add the bag to the heated water bath using the displacement method. If using jars, screw the cap on finger-tip tight, or attach cap and clips. Cook for 45 minutes, up to 1 hour.ORSimply add all the ingredients, including zest, to a sous vide safe bag, seal and cook, as above. You will need to agitate the bag a couple times throughout the cook and blend post cook, in this scenario.
Prepare an ice bath close to the end of the cook. Once cooked, remove the curd from the water bath and shake the contents. If you prefer a smoother texture, strain off the zest. Place the cooked curd in the prepared ice bath to cool down for about 20 minutes. Transfer to an airtight container and refrigerate for at least 6 hours. Best when consumed within 2 weeks.