Add lemon rind to sugar and rub together, stand aside for 3 to 4 minutes.
In Magimix Cook Expert add the whisked eggs, lemon and sugar mixture, and lemon juice.
Set to 80ºC and Speed 3 for 5 minutes.
Mixture will cook and thicken.
After 5 minutes, increase temperature to 82ºC.
Add butter cubes, one by one, and keep on speed 3 for 3 minutes until butter has been incorporated.
Set in jar or container and cool in refrigerator.

Spread generously on toasted bagels and enjoy!