Combine the lemon zest and sugar in the container of a food processor.

Process until the zest is very fine.

In a medium bowl, stir together the zest mixture and milk until sugar has dissolved.

Then stir in the lemon juice.

In a separate bowl, whip the double cream until stiff but not grainy.

Gently fold the whipped cream into the lemon mixture until blended.

Pour the mixture into a suitable cake or loaf tin.

Now cover with cling film.

Freeze for 3 hours, or until firm.