01 - Pour heavy cream and sugar into a medium saucepan. Place over medium heat, stirring gently until sugar completely dissolves.
02 - Bring mixture to a gentle boil, then reduce heat and simmer for 3 minutes. Stir occasionally to prevent overflow and ensure even heating.
03 - Remove saucepan from heat immediately. Stir in lemon zest and fresh juice until fully incorporated.
04 - Let mixture cool for 5 minutes. Pour through fine sieve into a pitcher to remove zest pieces for smoother texture. Divide evenly among 4 serving glasses or ramekins.
05 - Refrigerate for at least 3 hours until posset firms completely. The texture should be silky and hold its shape when spooned.
06 - Top each posset with fresh berries and mint leaves immediately before serving. Serve chilled.