Place the lemon zest, juice, eggs, sugar, and salt in a high-speed blender. Cover and blend for 5 minutes on the highest speed.
Reduce the speed to medium, remove the lid plug, and carefully add the butter one cube at a time. Once all the butter is added, blend for 30 seconds more until glossy.
Remove the lid carefully (steam will be releasing) and transfer the curd to a glass jar or other heat-proof container to cool to room temperature, about 20 minutes. Cover and refrigerate to thicken and set overnight.
