Pour the cream into a medium saucepan and add the sugar.
Set over medium heat and stir until the sugar has dissolved.
Bring to a simmer and the moment it start to boil, remove from the heat then stir in the lemon juice and zest.
At this point you can strain the lemon posset mixture through a fine-mesh strainer but I don't bother.
Transfer the mixture to small serving dishes like ramekins, jars or bowls then place in the fridge and allow to chill and set for at least 6 hours but ideally overnight.