01 - Pour heavy cream and granulated sugar into a medium saucepan. Place over medium heat, stirring gently until sugar completely dissolves.
02 - Continue heating the mixture until it just begins to simmer. Do not allow to boil. Remove immediately from heat once bubbles form around edges.
03 - Stir in fresh lemon juice and grated zest. The acid will cause the cream to thicken slightly as it reacts, creating the posset's signature texture.
04 - Let mixture cool at room temperature for 10 minutes. Pour evenly into 4 individual ramekins or dessert glasses.
05 - Refrigerate for at least 3 hours until fully set with a silky, pudding-like consistency. The posset should hold its shape when spooned.
06 - Serve chilled. Optional garnishes include fresh berries, additional lemon zest, or a shortbread cookie on the side.