Combine heavy cream and granulated sugar in a medium saucepan over medium heat. Stir gently until the sugar dissolves and the mixture simmers softly, about 5 minutes.

Remove from heat and add the freshly grated lemon zest and lemon juice, stirring well to blend all the flavors. Allow the mixture to cool for about 10 minutes.

Pour the cooled mixture into individual serving glasses or ramekins. Cover them with plastic wrap to keep everything fresh.

Refrigerate for at least 4 hours, or until the posset has set into a smooth, firm texture.

Garnish with fresh berries and mint leaves just before serving.