1. Make the lemon zest by grating one of the lemons using the cheese grater.
2. Beat together the eggs, egg yolks and Zùsto until solid.
3. Transfer the mixture to a saucepan and add the zest and lemon juice.
4. Warm over a low heat and continue to stir until smooth.
5. Remove the bowl from the heat and mix in the chopped butter.
6. Divide into glass jars, allow to cool, seal with a lid and then place in the refrigerator.

Enjoy!