Gather the ingredients.
Finely grate the zest off of 2 large lemons and juice the fruit, removing all seeds. You should get about 4 teaspoons of zest and ½ cup juice.
Pour the ½ cup of lemon juice into a small saucepan. Add the grated zest and ⅔ cup superfine sugar . Stir well to combine and bring the mixture to a slow, gentle simmer, about 4 minutes. Remove from heat and reserve.
In a medium-sized pot, bring 2 cups double cream to a gentle boil over low heat and allow to simmer for 5 minutes. Make sure to cook the cream slowly, as a fast boil will spoil the cream and split it. Remove from heat.
Slowly whisk the lemon syrup into the hot cream. Strain the mixture into a clean measuring cup.
Let the posset cool slightly and pour into small ramekins or glasses. Bring to room temperature.
Chill in the refrigerator for at least 4 hours and up to overnight. The cream will become silky and thick. Remove from the refrigerator and leave at room temperature for at least 5 minutes before serving.
Decorate with fresh berries and serve.
