Warm the cream and sugar

• Pour the double cream into a saucepan and add the caster sugar.
• Heat gently, stirring with a whisk, until the sugar has completely dissolved and the cream just comes to a simmer.

Add the lemon

• Take the pan off the heat and stir in the lemon zest and lemon juice.
• Whisk well and let it sit for a couple of minutes, then whisk again.

Fill the glasses

• Pour the mixture through a sieve into a jug or bowl.
• Divide between serving glasses or ramekins.

Chill until set

• Cover and refrigerate until the posset is firm and set.