01 - Pour heavy cream and granulated 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 exactly 3 minutes. Stir occasionally to prevent scorching and watch carefully to avoid overflow.
03 - Remove saucepan from heat immediately. Stir in fresh lemon zest and juice until thoroughly incorporated.
04 - Let mixture cool for 5 minutes. For smoother texture, strain through fine sieve into a pitcher to remove zest pieces. Divide evenly among 4 serving glasses or ramekins.
05 - Refrigerate for at least 3 hours until completely set and firm to the touch.
06 - Top each posset with fresh berries and mint leaves just before serving.