Put the cream in a saucepan with the sugar and gently heat, stirring vigilantly, until the sugar has melted. Be careful as this can boil over very quickly.

Bring slowly to the boil and simmer for 5 minutes. Stir in the lemon zest and juice.

Turn off the heat and divide between pots, ramekins or glasses and cool to room temperature.

Carefully cover and chill for at least three hours, or up to 24 hours.