01 - Pour heavy cream and sugar into a medium saucepan, stirring to combine.
02 - Set saucepan over medium heat, stirring gently until sugar completely dissolves.
03 - Bring mixture to a gentle boil, then reduce heat and simmer for exactly 3 minutes. Stir frequently to prevent overflow.
04 - Remove from heat immediately. Stir in lemon zest and juice until fully incorporated.
05 - Let mixture cool for 5 minutes. For smoother texture, strain through fine sieve into a pouring jug to remove zest.
06 - Divide mixture evenly among 4 small serving glasses or ramekins.
07 - Refrigerate for at least 3 hours until completely firm and set.
08 - Top each posset with fresh berries and mint leaves just before serving.